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/system-sections.css

@@ -1,18 +1,18 @@
-/* ─── SYST3M section panels — shared by the dashboard + /core.html ──
-   The four SYST3M panels (rebuild queue, meta inputs, kept state,
-   container load) render on /core.html (their renderers live in
-   core.js, carved out of the dashboard in a prior refactor). These
-   section-internal rules used to live in dashboard.css and were
-   pulled in by /core.html via a wholesale `@import "./dashboard.css"`,
-   which dragged the entire ~39kb dashboard stylesheet into the C0R3
-   bundle.
+/* ─── SYST3M/BU1LDS section panels — shared by dashboard, /core.html,
+   and /builds.html ──────────────────────────────────────────────────
+   The rebuild queue, meta inputs, kept state, and container-load panels
+   render on /core.html; rebuild queue + meta inputs + live-log also
+   render on /builds.html (the build lifecycle hub). These
+   section-internal rules used to live in dashboard.css and were pulled
+   in by /core.html via a wholesale `@import "./dashboard.css"`, which
+   dragged the entire ~39kb dashboard stylesheet into the bundle.
 
-   They now live here and are `@import`ed by BOTH core.css and
-   dashboard.css. /core.html gets only this small file instead of all
+   They now live here and are `@import`ed by core.css, dashboard.css,
+   and builds.css. Each page gets only this small file instead of all
    of dashboard.css; the dashboard keeps the rules (a couple are still
    referenced from dashboard JS — `.rqe-source*` by the schedules view,
    and `.hive-stats-table`, which already lives in common.css and is
-   loaded by both pages). Behaviour-preserving: identical rules, same
+   loaded by all pages). Behaviour-preserving: identical rules, same
    custom properties from colors.css / theme.css / common.css.
 
    The selectors here are uniquely named to these panels and are not
@@ -196,6 +196,75 @@
   cursor: default;
 }
 
+/* ─── running-rebuild live log (renderRebuildLiveLog in builds.js) ──────────
+   Streams the currently-running rebuild's build log inline under the queue.
+   Hidden (native `hidden` attr) when nothing is building. Used on
+   /builds.html; lives here (not in builds.css) so it can be shared if
+   the dashboard ever gains an inline live-log view. */
+.rebuild-live-log {
+  margin-top: 0.8em;
+  border: 1px solid var(--purple-dim);
+  border-radius: 4px;
+  background: color-mix(in srgb, var(--crust) 70%, transparent);
+}
+.rebuild-live-log-header {
+  display: flex;
+  align-items: center;
+  gap: 0.4em;
+  padding: 0.4em 0.6em;
+  font-size: 0.85em;
+  border-bottom: 1px solid var(--border);
+}
+.rebuild-live-log-toggle {
+  background: transparent;
+  border: 0;
+  color: var(--muted);
+  cursor: pointer;
+  font-family: inherit;
+  font-size: 1em;
+  padding: 0 0.2em;
+}
+.rebuild-live-log-toggle:hover { color: var(--fg); }
+.rebuild-live-log-title { color: var(--muted); }
+.rebuild-live-log-raw {
+  margin-left: auto;
+  color: var(--purple);
+  text-decoration: none;
+  font-size: 0.9em;
+}
+.rebuild-live-log-raw:hover { text-decoration: underline; }
+.rebuild-live-log-badge {
+  font-size: 0.75em;
+  font-weight: bold;
+  padding: 0.05em 0.5em;
+  border-radius: 999px;
+  letter-spacing: 0.05em;
+}
+.rebuild-live-log-badge.rll-running {
+  color: var(--amber);
+  background: color-mix(in srgb, var(--amber) 18%, transparent);
+}
+.rebuild-live-log-badge.rll-ok {
+  color: var(--green);
+  background: color-mix(in srgb, var(--green) 18%, transparent);
+}
+.rebuild-live-log-badge.rll-fail {
+  color: var(--red);
+  background: color-mix(in srgb, var(--red) 18%, transparent);
+}
+.rebuild-live-log-output {
+  margin: 0;
+  padding: 0.5em 0.7em;
+  max-height: 22em;
+  overflow-y: auto;
+  white-space: pre-wrap;
+  word-break: break-word;
+  font-family: "JetBrains Mono", "Fira Code", "Cascadia Code", "Source Code Pro", monospace;
+  font-size: 0.8em;
+  line-height: 1.4;
+  color: var(--fg);
+}
+
 /* ─── SYST3M › C0NT41N3R L04D: live cgroup cpu/mem ─────────────────────────────
    Reuses the shared `.hive-stats-table` styling (in common.css); only
    the inline meter bar is new. */