feat(desktop): run the live local gateway

[kev1n77]

Summary

• start the OpenAI-compatible local Gateway at 127.0.0.1:8787 from the Tauri desktop lifecycle
• process request events through Capture Policy, adapters, and SQLCipher, then notify React with capture-updated
• add pause/resume recording without interrupting transparent forwarding and surface runtime errors in Health
• preserve the selected request while live captures refresh the list and remove the legacy seeded demo from real workspaces
• eagerly drive incoming request bodies through a bounded forwarding channel so failed upstream connections still retain small complete requests
• update the engineering tracker to 28% with CAP-001/002 complete and APP-003 at 70%

Runtime verification

• launched the Windows Tauri debug app and confirmed the desktop process listened on 127.0.0.1:8787
• sent an OpenAI Responses request with header, query, and body canaries while the upstream returned 502
• verified the live workbench showed gpt-5.2, responses.create, and Verified runtime capture
• scanned SQLCipher database, SHM, and WAL files and found no plaintext canaries

Automated verification

• cargo fmt --all -- --check
• cargo test --workspace --all-targets
• cargo clippy --workspace --all-targets -- -D warnings
• cargo fmt --manifest-path apps/desktop/src-tauri/Cargo.toml -- --check
• cargo test --manifest-path apps/desktop/src-tauri/Cargo.toml
• cargo clippy --manifest-path apps/desktop/src-tauri/Cargo.toml --all-targets -- -D warnings
• npm run desktop:check
• npm run desktop:build
• python -m unittest discover -s sidecars/mitmproxy/tests -v