feat(sync): link and detach prompt resources

[ctawiah]

Context

After a workspace exists, users need to connect prompts that already live elsewhere in the repository and stop tracking resources without mutating LaunchDarkly. This change contains those two lifecycle workflows.

What changes

• Links a repository prompt through the plain-markdown adapter.
• Asks only for destination metadata that cannot be derived from the source file.
• Creates the corresponding .launchdarkly wrapper.
• Detaches selected wrappers and manifest entries while leaving LaunchDarkly and referenced source files unchanged.

Review focus

• Does linking preserve the external file as the content source?
• Are existing server and local variation keys protected from overwrite?
• Does detach remove only sync-owned state?

Verification

• go test ./internal/sync/...
• git diff --check

Related changes

Review the stack in this order:

1. Sync foundations
2. Prompt reference workspaces
3. Prompt sync manifests
4. Local prompt workspaces
5. Bootstrap prompt workspaces
6. Link and detach prompt resources
7. Prompt reconciliation
8. Prompt sync orchestration
9. Prompt sync command

---

Note

Overview
Adds link and detach workflows for prompt sync: connect an existing repo file to a LaunchDarkly variation via a local wrapper, or drop local tracking without touching LaunchDarkly or referenced sources.

Link (internal/sync/link) walks an interactive flow (project → config → model config, plus any missing key/name/content), parses the source through the plain-markdown adapter, validates destination (mode match, no duplicate server/local keys), then writes a .launchdarkly wrapper that points at the external file. Empty prompts can be filled only after validation; failed wrapper creation rolls the source file back. Create exposes the same path with a pre-selected destination for tests/CLI.

Detach (internal/sync/detach) lists the union of manifest entries and on-disk wrappers, multi-selects resources in the terminal, updates the manifest first, deletes local variation wrappers when present, and restores the manifest if deletion fails. Referenced prompt files are left intact.

synclocal.ReplaceFileAtomically reuses the existing staged-rename + content-snapshot check so link (and similar callers) cannot clobber a file that changed after read.

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[nieblara]

NICE!

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