feat(dashboard): add annotation mode

[pavelfeldman]

Summary

• Adds a third "Annotate" dashboard mode alongside Read-only and Interactive for drawing rectangular regions with text comments on top of the live screencast.
• Draw by click-drag; click a rectangle to select and drag; eight resize handles; arrow keys nudge by 5px (1px with Shift); Del removes; double-click or click label to edit text.
• Enter saves text; Shift/Ctrl/Cmd+Enter inserts a newline; Escape cancels/deselects in progressive layers. Submit emits a JSON payload with all annotations and viewport dimensions.
• Screencast frames are frozen while annotating so rectangles stay aligned with the content being annotated.

[github-actions]

Test results for "MCP"

6051 passed, 982 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

1 failed
❌ [playwright-test] › ui-mode-test-network-tab.spec.ts:395 › should copy network request @windows-latest-node20

5 flaky

⚠️ [chromium-library] › library/video.spec.ts:275 › screencast › should capture navigation `@chromium-ubuntu-22.04-node24`
⚠️ [chromium-library] › library/video.spec.ts:719 › screencast › should work with video+trace `@chromium-ubuntu-22.04-node22`
⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:1080 › cli codegen › should not throw csp directive violation errors `@firefox-ubuntu-22.04-node20`
⚠️ [firefox-page] › page/page-wait-for-function.spec.ts:104 › should work with strict CSP policy `@firefox-ubuntu-22.04-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:185 › should show snapshots for steps `@windows-latest-node20`

39186 passed, 847 skipped

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Merge workflow run.