feat(builds): add /builds.html — build lifecycle hub (closes #1999)

New standalone page /builds.html consolidating rebuild queue, meta
inputs, and build log history into one place, with a new 'Builds' home
tile linking to it. Addresses mara's request: new sub-page with a new
home tile, all three items moved there.

Changes:
- builds.html: new page with three sub-tabs: R3BU1LD QU3U3, M3T4 1NPUTS,
  BUILD L0GS. Same minimal-chrome header + createTabStrip pattern as core
  and logs pages.
- builds.js: new bundle combining rebuild queue renderer (from core.js),
  meta inputs renderer (from core.js), rebuild-live-log renderer (from
  core.js), and build log history renderer (from logs.js). Deep-links to
  /builds.html?id=N#buildlogs. Count pill id: builds-tab-count-rebuild.
  BUILD L0GS tab lazy-loads on first activation.
- builds.css: @imports system-sections.css (rebuild queue + meta inputs +
  live-log styles) and logs.css (build-logs-* component styles).
- build.mjs: register builds.js, builds.css, builds.html.
- core.html: remove R3BU1LD QU3U3 + M3T4 1NPUTS tabs (now on builds.html).
  Default tab changes to K3PT ST4T3.
- core.js: remove renderMetaInputs, renderRebuildQueue + helpers,
  renderRebuildLiveLog + live-log state, elapsed-time tickers,
  updateRebuildCount, and the rebuild_queue/meta_inputs SSE handlers.
  Remove openBuildLogStream + util imports no longer needed.
- core.css: remove .rebuild-live-log-* rules (moved to system-sections.css
  so builds.css can share them via @import).
- system-sections.css: add .rebuild-live-log-* styles (moved from core.css);
  update comment to mention builds.html.
- logs.html: remove BUILD tab + pane (moved to builds.html).
- logs.js: remove fetchBuild(), fmtTs, fmtDuration, openBuildLogStream
  import, and rebuild_queue_changed SSE debounce. Default tab: 'agent'.
  SSE stream retained for audit_entry_added live-appends.
- index.html: add Builds tile (🔨, rebuild queue · meta inputs · build
  logs); update Core tile desc to 'kept state · container load'; update
  Logs tile desc to remove 'build'.

frontend/packages/dashboard/src/logs.html

@@ -14,14 +14,12 @@
 
   <!-- Minimal chrome: back link + sub-tab strip.
        Same pattern as flow.html — no full dashboard tabbar. Back link
-       points to the H0M3 hub (served at /), not the dashboard. -->
+       points to the H0M3 hub (served at /), not the dashboard.
+       Three sub-tabs: AGENT, SYSTEM, AUDIT. Build log history has moved
+       to /builds.html (the build lifecycle hub). -->
   <header class="page-header">
     <a class="page-back" href="/">← home</a>
     <nav class="hive-tabbar logs-tabbar" id="logs-tabbar" role="tablist">
-      <a class="hive-tab" id="logs-tab-build" href="#build" role="tab"
-         aria-controls="logs-pane-build" data-tab="build">
-        <span class="logs-tab-label">BUILD</span>
-      </a>
       <a class="hive-tab" id="logs-tab-agent" href="#agent" role="tab"
          aria-controls="logs-pane-agent" data-tab="agent">
         <span class="logs-tab-label">AGENT</span>
@@ -39,18 +37,6 @@
 
   <main class="logs-main">
 
-    <!-- BUILD: all-agents build log history. Lists recent nix build /
-         nixos-container invocations across all agents, with
-         click-to-expand full stdout+stderr. Backed by
-         GET /api/build-logs?limit=30. -->
-    <section class="logs-pane" id="logs-pane-build" data-tab-pane="build"
-             role="tabpanel" aria-labelledby="logs-tab-build">
-      <div class="logs-toolbar">
-        <button type="button" class="btn btn-restart" id="build-refresh">↻ refresh</button>
-      </div>
-      <div id="build-list"><p class="meta">loading…</p></div>
-    </section>
-
     <!-- AGENT: journald viewer for a specific agent container.
          Agent selector + unit filter + line count. Backed by
          GET /api/journal/{agent}?unit=<unit>&lines=N. -->