feat: add media capture APIs, wasm example, and CI coverage

[niklabh]

Implement Phase 1 Media Capture from the roadmap: camera (open/close, RGBA frames, dimensions), microphone (mono f32 ring buffer, sample rate, read_samples), primary-display screenshot (RGBA + dimensions), and api_media_pipeline_stats (camera frame count + mic ring depth).

Host (oxide-browser):

• New module media_capture.rs registering imports under oxide; HostState gains media_capture: Arc<Mutex>.
• Use nokhwa (input-native + camera-sync-impl for Send), cpal for input, screenshots for display capture; rfd dialogs before hardware access.
• pub(crate) write_guest_bytes for guest memory writes from media_capture.

SDK (oxide-sdk):

• FFI + safe wrappers: camera_, microphone_, screen_capture*, media_pipeline_stats; crate docs table updated.

Example (examples/media-capture):

• PNG-encode RGBA for canvas_image (host decodes encoded images only).
• UI: camera preview, mic level meter, screenshot thumbnail, pipeline footer.

Other:

• examples/index: Media Capture card linking to media_capture.wasm.
• CI: libv4l-dev (Linux camera); wasm32 check for media-capture example.
• ROADMAP: mark Media Capture items complete.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 43737cc5-f553-42fd-9305-e7fd53f2834a

📥 Commits

Reviewing files that changed from the base of the PR and between b0c43c4 and e663591.

📒 Files selected for processing (11)

• .github/workflows/ci.yml
• Cargo.toml
• ROADMAP.md
• examples/index/src/lib.rs
• examples/media-capture/Cargo.toml
• examples/media-capture/src/lib.rs
• oxide-browser/Cargo.toml
• oxide-browser/src/capabilities.rs
• oxide-browser/src/lib.rs
• oxide-browser/src/media_capture.rs
• oxide-sdk/src/lib.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/media-capture

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