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/builds.css

@@ -0,0 +1,26 @@
+/* ─── /builds.html — BU1LDS page ────────────────────────────────────
+   The build lifecycle hub: rebuild queue + live log, meta inputs, and
+   build log history on one page. Carved out of /core.html (rebuild
+   queue + meta inputs) and /logs.html (BUILD tab).
+
+   Imports system-sections.css for rebuild queue + meta inputs + live-log
+   component styles, and logs.css for the build-logs-* component styles.
+   Body-scoped `.logs-shell` rules in logs.css don't apply here
+   (`.builds-shell` body); only the build-logs-* component rules are used. */
+@import "./system-sections.css";
+@import "./logs.css";
+
+body.builds-shell {
+  margin: 0;
+  padding: 0;
+}
+
+.builds-tabbar {
+  flex: 1;
+}
+
+.builds-main {
+  padding: 1.2em 1.5em 2em;
+}
+
+.builds-pane[hidden] { display: none; }