feat(channels): move diagnostics into Channel Settings

[wesbillman]

Summary

• Make the channel three-dot button open Channel Settings, with channel details first and diagnostics collapsed below. Existing unread, refresh, live-status, outbox and timing controls keep their behavior; actionable connection failures stay visible in the conversation.
• Reuse the existing responsive side-panel layout and shared controls. Close/Escape restores focus, navigation clears Settings, and temporary Settings access preserves thread/link state. Terminal and Settings openings do not obscure each other.
• No backend, protocol, channel-editing API or new permission changes.

Screenshot

Approved during the manual feedback round; cropped to the Settings panel to omit surrounding chat/sidebar content.

Notification-test synchronization follow-up

• Head c135ee86122c9f82cbbdc9a4c951e0ec686bcc35 adds the test-only correction for the sole remaining failure in run 35881351396: notification click navigation could still be opening after Appearance rendered. The test now polls for completion, as the neighboring notification journey already does, preserving both visible-heading and opened assertions. No production code, sleeps, retries or timeout changes.
• Full notifications.spec.mjs passed 14/14 across Chromium and WebKit on this clean commit; required commit/push hooks passed. Earlier channel/measurement repair checks passed hosted CI at 6e8ea383. The new head remains subject to hosted CI; no claim that one local pass eliminates every possible flake.
• Main remains 56778764 and is included. This fix ships with this PR, not a prerequisite PR.

CI repair and main integration

• Final repaired head: 6e8ea383e027f9d2d01c55ddef067f18194cebbd, includes main 56778764 (fetched again before push). Clean merges; no rewritten commits.
• Migrated timing-export setup into Channel Settings; targeted the actual overlay ancestor for layout stacking; replaced deleted diagnostics-popup token probing with real Settings-panel surface checks. Also restored silently missing stream-evidence timing attachments while keeping raw capture before opening diagnostics. No production behavior, hook policy, retries, tolerances or timing budgets changed in the repair.
• At that clean final head, complete affected files passed on local macOS Chromium + WebKit: 10 measurement checks (channel-opening, scroll) and 58 functional checks (design-system, layout, channel-settings, sidebar-unread, message-navigation). Both stream measurement exports and all ten sidebar exports are valid JSON; no caught evidence errors in the functional report.
• Independent repair review passed. Mandatory commit/push hooks passed. The initial CI failures provide fail-before evidence for the three migrated test consumers; their complete files now pass locally. Full hosted CI at the new head remains pending; no native or full-suite local rerun claimed.

Original validation (before main integration)

• Built and exercised the live frontend before writing/running tests; Wes approved the UI.
• Full frontend Vitest: 2,248 passed / 214 files on the final production diff. Subsequent edit only corrected the drawer-test fixture's revision type from number to string; required push checks reran the affected tests.
• Affected browser files: 62 passed, Chromium + WebKit. After adding explicit thread/profile DOM-retention and scroll assertions, the complete message-navigation file passed again: 26 passed across both engines.
• Required pre-commit and pre-push hooks passed at 2fb0ddc: formatting/lint, TypeScript, related Vitest (29 tests), design types and guards. Independent lifecycle review passed.
• Added one browser journey (two engine executions) for real responsive geometry, focus return and navigation disposal. Added four component/hook tests; removed no cases. Existing unread/live/navigation journeys now enter through Channel Settings. No fail-then-pass mutation run; native packaging and the full browser/native suites were not run locally. Broad CI remains the merge gate.

Originating Buzz channel: ffce3697-facf-4e35-a191-54b0b5ff903a

buzz://message?channel=ffce3697-facf-4e35-a191-54b0b5ff903a&id=81db8cc57e3db46b58b51e5593dc37ae12fe8998b56d817b01187a136eef59e8