fix(desktop): manual tool previews via status stack

[OutThisLife]

Summary

• No auto-open. Tool results no longer push HTML/localhost artifacts into the right-rail preview on tool.* events. Session-switch restore of a user-opened preview and refresh-when-already-open on file diffs are preserved.
• Status stack link. Detected preview artifacts surface as a single always-visible row in the composer status stack (not an inline card, not a collapsible group). Row toggles the preview rail open/closed; external-browser opens file:// via shell.openExternal, not openPath.
• Removed inline preview card from tool rows; detection feeds the status stack from the same previewTarget the card used.
• Polish: drop inline code border; halve expanded tool block radius.

Test plan

• Agent writes/edits .html → status stack shows preview row; rail does not auto-open
• Click row → rail opens; click again (Hide) → rail closes
• External-browser button opens local HTML in the system browser
• Dismiss (X) removes the row without affecting an open rail
• Inline demo.html in prose has no border; expanded tool diff has tighter corners
• vitest run apps/desktop/src/store/preview-status.test.ts apps/desktop/src/store/preview.test.ts apps/desktop/src/app/session/hooks/use-preview-routing.test.tsx

[github-actions]

🔎 Lint report: bb/desktop-tool-preview-cleanup vs origin/main

ruff

Total: 0 on HEAD, 0 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 0 pre-existing issues carried over.

ty (type checker)

Total: 11478 on HEAD, 11480 on base (✅ -2)

🆕 New issues (1):

Rule	Count
invalid-assignment	1

First entries

tests/run_agent/test_credits_notices_toggle.py:76: [invalid-assignment] invalid-assignment: Object of type `None` is not assignable to attribute `_credits_session_start_micros` of type `int`

✅ Fixed issues (2):

Rule	Count
unresolved-attribute	2

First entries

tests/run_agent/test_credits_notices_toggle.py:76: [unresolved-attribute] unresolved-attribute: Unresolved attribute `_credits_session_start_micros` on type `AIAgent`
run_agent.py:2984: [unresolved-attribute] unresolved-attribute: Object of type `Self@get_credits_spent_micros` has no attribute `_credits_session_start_micros`

Unchanged: 6051 pre-existing issues carried over.

Diagnostics are surfaced as warnings — this check never fails the build.