Add public Forums sub-app and shared forum editing

src/apps/forums/README.md

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+# Public forums
+
+The Forums app is available at `/forums` on the platform host and at `/` when
+`EnvironmentConfig.SUBDOMAIN` is `forums`. Its single domain root contains the
+category and thread routes so deep links work on both hosts. `ForumsApp` renders
+the child routes through the platform router context, matching the sub-app routing
+contract (a bare React Router `Outlet` does not render these declarations). Hosting must serve
+the Platform UI SPA for the forums hostname and its nested routes.
+
+The design source is [Forums in Figma](https://www.figma.com/design/I45k1Djt2XkYY692wopp3C/Forums?node-id=14382-6451).
+The pages use Figtree headings and Nunito Sans body text, the 1200 px page width,
+280 px sidebar, 32 px column gap, 32/40 px title typography, supplied Figma SVG
+assets, and the existing universal header/footer. Forum controls use a scoped
+border-box reset so their Figma dimensions do not depend on another app's CSS.
+Typography and paragraph defaults use low-specificity selectors so shared card
+titles, action buttons, and Markdown keep their own styles. Mobile stacks the
+sidebar and content at 767 px, uses 28/36 px headings, and shows the compact
+breadcrumb and category creation card on thread pages. Desktop headings remain
+32/40 px. My Drafts is intentionally omitted.
+
+`ForumsPage` renders the category index, category topic list, search, Watching,
+thread details and creation flow. It reads `/v6/forums/public/categories` and
+`/v6/forums/public/topics`; normal topic/post commands are shared with challenge
+forums. Search, pagination, watches and category visibility are enforced by the
+API. Authenticated response cache keys include the member ID and roles. Legacy
+non-login author IDs retain their handle/initials and are excluded from numeric
+member-profile lookup batches.
+
+Guest pages require no login. Interaction controls send guests through the
+existing login flow with the current URL as their return location. Signed-in
+members see creation/reply controls according to API permissions; locks still
+apply. Author editing, administrator deletion, announcements, reactions and
+watching use the existing services rather than separate public implementations.
+
+The exported `ForumMember`, `ParticipantGroup`, `ForumTopicCard`,
+`ForumTopicView`, `ForumTopicEditModal` and `MarkdownEditor` components in
+Opportunities are shared. Public detail uses `contentOnly` to supply its own
+Figma header/sidebar and `onSignIn`/`onWatch` callbacks for guest interaction and
+thread-wide watching. This keeps rated handles, mentions, nested replies,
+quoting, sanitized Markdown, previews and moderation behavior consistent.
+
+The common Markdown toolbar also supports headings, lists, strike-through,
+restricted text sizes/alignment, links, images, tables, mentions and expanding
+the editor. `uploadForumAttachment(file)` uses the existing environment's
+Filestack API key/CNAME/security configuration, enforces a 25 MiB limit and
+returns escaped Markdown using an HTTPS URL. Files upload when selected; failures
+stay beside the editor. Raster image formats render inline; SVG/other files use
+download links. A deployment must supply a valid `FILESTACK_API_KEY` (and the
+existing security policy/signature where required). Imported attachment links
+continue to use their original Filestack URLs.
+
+Deploy the companion forums-api-v6 public-forums change before enabling this
+app. It adds inherited category permissions, optional public reads, catalog
+endpoints and the insert-only Vanilla migration. A denied category must remain
+denied in the API even when a user enters its URL directly.
+
+From this project folder, run `nvm use`, `yarn lint`, `yarn run build`, and:
+
+```sh
+CI=true yarn test:no-watch --runInBand \
+  --testPathPattern='ForumsApp.spec|forums.routes.spec|ChallengeForum.spec|ForumMarkdown.spec|forum.service.spec|forum-attachments.service.spec|forum-mention|member-profile.service'
+```
+
+On memory-constrained build runners use `NODE_OPTIONS=--max-old-space-size=8192`
+for the production build. Before production cutover, compare the index,
+category, thread and composer screens in a connected desktop/mobile browser;
+verify guest login return paths and real Filestack uploads with configured keys.

src/apps/forums/index.ts

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+export { forumsRoutes } from './src/forums.routes'

src/apps/forums/src/ForumsApp.spec.tsx

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+/* eslint-disable import/no-extraneous-dependencies, ordered-imports/ordered-imports, global-require */
+import '@testing-library/jest-dom'
+import { render, screen } from '@testing-library/react'
+import { MemoryRouter } from 'react-router-dom'
+
+import { EnvironmentConfig } from '~/config'
+import { RouterProvider } from '../../../libs/core/lib/router/router-context/router.context-provider'
+import PlatformRouter from '../../platform/src/platform-router/PlatformRouter'
+
+import { forumsRoutes } from './forums.routes'
+
+jest.mock('~/config', () => ({
+    AppSubdomain: { forums: 'forums' },
+    EnvironmentConfig: { SUBDOMAIN: 'platform' },
+    ToolTitle: { forums: 'Forums' },
+}), { virtual: true })
+jest.mock('~/libs/core', () => ({
+    ...jest.requireActual('../../../libs/core/lib/router/router-context/router.context'),
+    ...jest.requireActual('../../../libs/core/lib/router/router.utils'),
+}), { virtual: true })
+jest.mock('../../../libs/core/lib/profile', () => ({
+    profileContext: jest.requireActual('react')
+        .createContext({ initialized: true }),
+}))
+jest.mock('../../../libs/core/lib/auth', () => ({ authUrlLogin: () => '/login' }))
+jest.mock('~/libs/shared', () => ({ RestrictedPage: () => <div>Restricted</div> }), { virtual: true })
+jest.mock('~/libs/ui', () => ({ LoadingSpinner: () => <div>Loading</div> }), { virtual: true })
+jest.mock('./ForumsPage', () => ({
+    __esModule: true,
+    default: () => {
+        const params = jest.requireActual('react-router-dom')
+            .useParams()
+
+        return <div>{params.categoryId || params.threadId || 'Forum index'}</div>
+    },
+}))
+
+describe('ForumsApp with the platform router', () => {
+    it.each([
+        ['platform', '/forums', '', 'Forum index'],
+        ['platform', '/forums', '/category/category-123', 'category-123'],
+        ['platform', '/forums', '/thread/thread-456', 'thread-456'],
+        ['forums', '', '', 'Forum index'],
+        ['forums', '', '/category/category-123', 'category-123'],
+        ['forums', '', '/thread/thread-456', 'thread-456'],
+    ])('renders the %s host at %s%s', async (host, root, path, expected) => {
+        EnvironmentConfig.SUBDOMAIN = host
+        // Route declaration tests verify each computed host root; exercise its real rendering contract here.
+        const routes = forumsRoutes.map(route => ({ ...route, route: root }))
+        render(
+            <MemoryRouter initialEntries={[`${root}${path}` || '/']}>
+                <RouterProvider allRoutes={routes} rootCustomer='' rootLoggedOut='' rootMember=''>
+                    <PlatformRouter />
+                </RouterProvider>
+            </MemoryRouter>,
+        )
+        expect(await screen.findByText(expected))
+            .toBeInTheDocument()
+    })
+})

src/apps/forums/src/ForumsApp.tsx

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+import { FC, useContext } from 'react'
+import { Routes } from 'react-router-dom'
+
+import { ToolTitle } from '~/config'
+import { routerContext, RouterContextData } from '~/libs/core'
+
+/** Renders the forum child routes supplied by the platform router on either host.
+ * @returns The matching index, category, or thread page. @throws Does not throw.
+ */
+const ForumsApp: FC = () => {
+    const { getChildRoutes }: RouterContextData = useContext(routerContext)
+
+    return <Routes>{getChildRoutes(ToolTitle.forums)}</Routes>
+}
+
+export default ForumsApp