feat(agent): in-UI log console + a real styling pass on the control page

- logbuf.py: bounded in-memory log ring buffer + a logging.Handler on the root
  logger; GET /logs serves it; the control page polls it into a console pane —
  so runs are monitorable without `docker logs`. worker now logs autoscale moves
  (one line per change, with jobs/s + util + VRAM) and job failures (job + image
  + reason); detectors already log load/disable.
- Restyled the whole control page: a proper dark layout with a header + live
  connection pill, cards (Control / Status / Logs), a styled Auto switch +
  worker stepper, status tiles, separate GPU-util and VRAM meters, and the log
  console. No longer feels like an afterthought; all the existing control hooks
  are preserved.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

agent/fc_agent/worker.py

@@ -9,6 +9,7 @@ That's the dial the operator turns to trade desktop responsiveness for speed.
 Stop (or shrinking the pool) RELEASES a slot's still-leased jobs immediately so
 orphaned work is re-picked at once rather than waiting out the lease.
 """
+import logging
 import threading
 
 import numpy as np
@@ -58,6 +59,8 @@ UTIL_HI = 96               # GPU util% considered saturated
 TPUT_MARGIN = 0.10         # a step up must beat the baseline by this to "help"
 REPROBE_TICKS = 5          # ticks to hold after settling before re-probing up
 
+log = logging.getLogger("fc_agent.worker")
+
 
 class _Slot:
     """One worker loop. `inflight` = jobs leased but not yet processed, so a
@@ -230,6 +233,7 @@ class Worker:
             dt = max(1e-3, now - prev_t)
             tput = (self.processed - prev_p) / dt
             prev_p, prev_t = self.processed, now
+            t0 = self._target
 
             g = gpumod.read_gpu() or {}
             mt = g.get("mem_total_mb") or 0
@@ -260,6 +264,12 @@ class Worker:
             else:
                 base_tput = None                     # settled → re-probe next cycle
 
+            if self._target != t0:
+                log.info(
+                    "autoscale: %d→%d workers (%.2f jobs/s · util %d%% · vram %d%%)",
+                    t0, self._target, tput, util, round(vram * 100),
+                )
+
     def _ensure_embedder(self, model_name: str):
         if self._embedder is not None:
             return self._embedder
@@ -400,15 +410,21 @@ class Worker:
                 # effort; no-ops if the server is still down, then the server's
                 # orphan-recovery reclaims it) and signal the loop to wait.
                 self._bump(transient=1)
+                log.info("curator unreachable — released job %s, backing off",
+                         job.get("job_id"))
                 self.client.release([job["job_id"]])
                 return False
             # A job-specific HTTP fault (404 image gone, 400) → fail it so it
             # doesn't re-lease forever.
             self._bump(errors=1)
+            log.warning("job %s (image %s) failed: %s",
+                        job.get("job_id"), job.get("image_id"), str(exc)[:200])
             self.client.fail(job["job_id"], str(exc)[:500])
             return True
         except Exception as exc:   # noqa: BLE001 — a genuine job fault: report it
             self._bump(errors=1)
+            log.warning("job %s (image %s) failed: %s",
+                        job.get("job_id"), job.get("image_id"), str(exc)[:200])
             self.client.fail(job["job_id"], str(exc)[:500])
             return True
         finally: