fix: announce camera focus changes

[mittalsonal]

Related Issue

Closes #2084

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Change Summary

• Added a polite, atomic screen-reader status region in the header for camera target updates.
• Added a shared cameraAnnouncement state value in the app provider.
• Updated camera focus/reset flows to announce clear targets such as Camera focused on AST-0042. and Camera returned to Earth.
• Added regression coverage for the polite live region.
• Tightened touched-file types so the edited files pass targeted lint cleanly.

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Suggested Area

Accessibility

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Core Files Changed

• src/components/Header.tsx
• src/lib/store.tsx
• src/__tests__/Header.test.tsx

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Verification

• No visible UI change; announcement is screen-reader-only.
• npm test -- --run src/__tests__/Header.test.tsx - passed, 1 test.
• npm run typecheck - passed.
• npx eslint src/components/Header.tsx src/lib/store.tsx src/__tests__/Header.test.tsx --format json - passed, clean result for touched files.
• npm run build - passed.
• git diff --cached --check - passed.

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AI Assistance Declaration

Did you use an AI tool to write or assist with this code OR Pull Request?

• Yes

• No

• Which AI Model did you use?: GPT-5 Codex

• Which Platform/Tool?: Codex

• What exactly did the AI do?: Assisted with repository inspection, implementation, tests, and verification commands.

• What exactly did YOU do?: Reviewed the assigned task, kept the change scoped, verified account/repo safety, and validated locally.

• What is the advantage of using this AI approach here?: Faster accessibility-focused implementation with regression coverage and repeatable verification.

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Reviewer Notes

• The status region starts empty and only announces after camera focus/reset changes.
• Existing local docs/ARCHITECTURE.md changes were not included in this PR.

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Local Verification Pledge

• I tested these changes in my local branch.
• I verified this code compiles into a standalone build and does not break existing production behavior.

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[mittalsonal]

Maintainer note: I checked the red statuses. The code-owned \ ypecheck\ job is passing, and local verification also passed for the focused test, targeted lint, typecheck, and build. The remaining red statuses appear to be repository integration/permission blockers rather than implementation failures: Vercel requires team authorization for fork deploys, and the auto-label workflow is failing with fork PR token permissions while trying to add labels. Happy to adjust anything code-related if you spot an issue during review.