feat(desktop): manage local runtime lifecycle

[tuzuminami]

Closes #107

What changed

• Move local API ownership into Tauri managed state with single-instance handling, child lifecycle cleanup, ownership nonce checks, and redacted runtime status.
• Add explicit, fail-closed recovery for port collisions, missing packaged sidecars, stale markers, and unverified marker quarantine.
• Harden backend child-process environments and expose a constant-time local runtime health endpoint.
• Add a least-privilege Tauri capability, recovery UI, development launcher, CI Rust runtime tests, and runbook coverage.

Validation

• ./scripts/test.sh
• ./scripts/lint.sh
• ./scripts/check_licenses.sh
• ./scripts/check_no_external_network.sh
• cargo check --locked --manifest-path apps/desktop/src-tauri/Cargo.toml
• cargo test --locked --manifest-path apps/desktop/src-tauri/Cargo.toml