feat(maestro): serve the web UI from the daemon

The browser reached the daemon through maestro-web, a second binary that
served the SPA and reverse-proxied /api/* — two TCP connections and a
WebSocket frame re-encode on every keystroke and every byte of PTY output.
On one machine that hop buys nothing.

The daemon now embeds the bundle and serves it off its own listener, behind
a default-on `web` feature. `--no-default-features` builds without pnpm or
node; MAESTRO_WEB_DIST still takes a prebuilt bundle.

The router's fallback answers an unmatched /api/* with 404 rather than the
SPA shell, so a client expecting JSON gets a status it can read instead of
HTML.

Removes maestro-web and the [web] config section. An existing [web] block
is ignored, not rejected. The installer deletes a leftover
maestro-web.service on upgrade.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Justfile

@@ -5,15 +5,15 @@
 dev:
     nix run .#dev
 
-# Build the maestro-web binary together with the SPA bundle it embeds.
+# Build the maestro binary together with the SPA bundle its daemon embeds.
 web:
     pnpm -C web install --frozen-lockfile
     pnpm -C web build
-    cargo build -p maestro-web --release
+    cargo build -p maestro --release
 
-# Run the web bundle in dev mode against a local daemon — Vite serves the
-# frontend with HMR, and `/api/*` is proxied directly to the daemon at
-# 127.0.0.1:7070 (see vite.config.ts).
+# Run the frontend in dev mode against a local daemon — Vite serves it with
+# HMR, and `/api/*` is proxied directly to the daemon at 127.0.0.1:7070
+# (see vite.config.ts).
 web-dev:
     pnpm -C web install
     pnpm -C web dev