feat(web): dedicated full-page log viewer + run lyra-web as a service

The inline log panel is cramped, especially on mobile. Add a standalone
mobile-first log page and serve the chat server under systemd like the dream
loop (the nohup process didn't survive cleanly).

- static/logs.html: full-page live log — level filter chips, text search,
  pause/resume with buffering, autoscroll toggle, color-coded levels, and the
  expandable "view full prompt" block (where the now-note is visible in context)
- server: GET /logs serves the page (FileResponse)
- index.html: "⛶ Full Log" button opens /logs in a new tab
- deploy/lyra-web.service: user service so the chat server is reboot-resilient

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyra/web/static/index.html

@@ -69,6 +69,7 @@
       <button id="newSessionBtn">➕ New</button>
       <button id="renameSessionBtn">✏️ Rename</button>
       <button id="thinkingStreamBtn" title="Show live activity log">📜 Live Log</button>
+      <a id="fullLogBtn" href="/logs" target="_blank" rel="noopener" title="Open the full-page log" role="button">⛶ Full Log</a>
     </div>
 
     <!-- Status -->