feat: cap-aware autoscaler + token-gated whole-instance tag reset (operator feedback)

Autoscaler (agent 2026-07-02.5): the buffer-occupancy signal alone would peg
downloaders at DL_MAX while the bandwidth CAP — not concurrency — is the real
constraint (8 streams sharing 8 MB/s move no more data than 4). Growth is now
gated on the pipe having headroom (net < 85% of cap) and a pipe pinned at the
cap (>= 95%) sheds streams down to 3; dead band prevents flapping. The UI hint
says 'holding at the bandwidth cap' and /status reports bw_capped, so the
behavior is legible without tests that need the ML stack.

Reset content tagging: stays a FULL-instance reset (operator's call), but now
lives in a fenced 'Danger zone' section on Cleanup and the apply is gated by a
preview-derived confirm token (mirrors the Tier-C bulk-delete pattern — stale
counts are rejected server-side). Copy no longer claims suggestions repopulate:
it says plainly the heads' training examples are deleted and re-tagging starts
fresh. Moved out of TagMaintenanceCard into DangerZoneCard.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/services/cleanup_service.py

@@ -726,7 +726,10 @@ RESETTABLE_TAG_KINDS = ("general", "character")
 
 def reset_content_tagging(session: Session, *, dry_run: bool = False) -> dict:
     """Count (dry_run) or DELETE every general + character tag so the operator
-    can re-tag from scratch (heads/CCIP repopulate suggestions).
+    can re-tag from scratch. NB: the deleted applications include the tagging
+    heads' training positives — suggestions do NOT repopulate on their own; the
+    heads retrain from whatever the operator re-tags. (The API route gates the
+    live run behind a preview-derived confirm token for exactly this reason.)
 
     PRESERVED: fandom + series tags and their series_page ordering. CASCADE on
     image_tag / tag_alias / tag_suggestion_rejection clears each deleted tag's