Admin UI epic

v0.2.0 delivers the optional local admin Web UI designed in #52 and implemented across #92–#97.

The embedded SvelteKit console now covers daemon and cache readiness, repository topology and independent coverage lanes, typed diagnostics, sync/RAG job supervision, maintenance and binding plan/apply controls, and a full-text versus hybrid Search Lab with bounded RAG repair. Light, Dark, and System themes share one documented visual system; System remains the default.

The admin listener remains disabled until gitcode-mcp admin open or an explicit service run --admin. It binds to loopback by default, shares the existing daemon/coordinator, and does not give the browser authority to read credentials, choose cache paths, install providers, delete data, or perform remote destructive writes. Node.js is not required to run the shipped binary or its embedded UI.

There are no cache migrations or breaking CLI/MCP changes in this release. Replacing the binary and restarting the service upgrades the UI atomically while preserving caches, bindings, jobs, and maintenance registrations.