[codex] Audit web backend parity

[kwannoel]

Summary

• Adds a web backend parity audit doc that maps the old desktop command/event surface to the current web frontend plus Axum backend runtime.
• Adds a Vitest regression guard that checks production frontend command literals have HTTP routes, verifies desktop command coverage, and blocks stale active docs.
• Updates README, architecture, keyboard docs, e2e scripts/config, and chat-mode comments to reflect the web frontend plus local backend setup.
• Applies mechanical Rust clippy cleanup for uninlined_format_args so cargo clippy -- -D warnings passes on the server crate.

Validation

• pnpm install --frozen-lockfile
• pnpm check (0 errors, existing Svelte a11y warnings remain)
• pnpm test (303 tests)
• pnpm build
• cd server && cargo fmt --check && cargo clippy -- -D warnings
• cd server && cargo test (291 lib, 4 CLI, 16 integration tests)
• pnpm exec playwright test --project=e2e e2e/specs/smoke.spec.ts
• bash -n dev.sh e2e/eval.sh
• git diff --check