dashboard: stream the running rebuild's build log inline in the queue

The C0R3 rebuild queue only linked out to the logs page (logs →). Add an
inline live-log panel under the queue that streams the currently-running
rebuild's build output, so the operator watches progress without leaving the
page.

One panel keyed to the running entry's build_log_id (the queue runs one build
at a time), reusing the build-log SSE the logs page already uses
(GET /api/build-logs/id/{id}/stream; frames stdout_append/stderr_append/done).
It lives in its own container (#rebuild-live-log) outside rebuild-queue-section
so the queue's per-row re-render — rows rebuild as the build step advances —
never tears down the open stream; it reconnects only when the running
build_log_id changes and won't reopen a stream that already sent done. Sticky-
bottom scroll, collapsible, live/ok/fail badge, raw download. Hidden when
nothing is building; each row keeps its logs → link for full history.

Frontend-only — no backend change (endpoint + build_log_id already existed).
Closes #1860.

frontend/packages/dashboard/src/core.html

@@ -55,6 +55,11 @@
       <div id="rebuild-queue-section">
         <p class="meta">loading…</p>
       </div>
+      <!-- Live build log of the currently-running rebuild (one runs at a
+           time). Managed by renderRebuildLiveLog in core.js, separate from
+           rebuild-queue-section so the queue's row re-render never disturbs
+           the open SSE stream. -->
+      <div id="rebuild-live-log" hidden></div>
     </section>
 
     <!-- M3T4 1NPUTS: select inputs to nix flake update in /meta/. -->