docs: refresh Agent screenshots and navigation

[priyansu-rout19]

The Agents guides still showed older controls and screenshots. Update 10 pages to match the current sidebar, setup, sessions, Inbox, sharing, and routine controls, and use 13 native PNG captures with matching captions and alt text.

The screenshots retain the workspace context needed to follow each workflow. Crops remove window edges, unrelated overlays, and account details without resizing or changing source pixels. The launch-review example identifies its fictional sample launch once, then follows the original example-led narrative. Session and routine instructions clarify when to use the dropdown and how to save a routine.

Remove the 13 replaced PNGs from public/images/agents/; no tracked source references them.

Validation

• npm run build and npm run types:check passed.
• Full MDX spelling check and git diff --check passed.
• All 10 affected localhost pages and all 13 PNG URLs returned HTTP 200. Image links, rendered dimensions, MIME types, and served file hashes matched the checked files.
• All 13 PNG crops matched their original source pixels and color profiles. Original screenshots were unchanged; output files contain no EXIF or text metadata.
• Reviewed screenshot boundaries, privacy, captions, and updated navigation against the captures and current Agent source.