feat(system-tags): process vs chrome groups + WIP provisional auto-apply (#1464)

Backend for the system-tag behavior refactor (milestone #157). editor screenshot
moves from chrome (hidden) to the PROCESS group (shown, like wip); wip+editor gain
provisional auto-apply so they stop needing endless manual identification —
without a runaway loop.

- tag.py: split PRESENTATION_SYSTEM_TAGS → CHROME_SYSTEM_TAGS (banner) +
  PROCESS_SYSTEM_TAGS (wip, editor screenshot).
- heads.py: generalize presentation_auto_apply_sweep → system_tag_auto_apply_sweep
  (mode chrome|process). Same Guard 1 (skip human/confirmed) + Guard 2 (ring-loud
  conflict → PresentationReview). process mode uses source 'process_auto' and does
  NOT hide (hide is a gallery-query effect of group membership).
- training_data._AUTO_SOURCES += 'process_auto' → the head never trains on its own
  auto-applied output; only wip_title/manual train it (the runaway break).
- ml_settings: process_auto_apply_enabled (OFF, opt-in) + threshold + conflict
  threshold. presentation_review.mode ('chrome'|'process'). Migration 0086.
- gallery_service: default-hide reads CHROME only (editor now shows); Explore
  neighbors exclude the whole PROCESS group.
- tasks/ml + celery beat: scheduled_process_auto_apply (daily, opt-in); prune
  covers both modes.
- api: ml_admin process_* CRUD+validation; hidden-review returns mode.
- tests: rename chrome sweep calls; new test_process_auto_apply (apply, guards,
  mode flag, no-self-train); gallery test asserts editor now visible.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/models/presentation_review.py

@@ -1,15 +1,17 @@
-"""PresentationReview — an auto-hidden presentation tag that ALSO looked like
-real content, flagged for operator review (milestone 141).
+"""PresentationReview — a system-tag the auto-apply sweep applied that ALSO looked
+like real content, flagged for operator review (milestone 141 + #1464).
 
-When the auto-apply sweep hides an image as chrome (banner / editor screenshot)
-but the image ALSO scores highly on a content head, it still hides it but records
-this row so the Hidden view can surface it ("⚠ also looks like <conflict tag>")
-for a keep-hidden / un-hide decision. Resolved rows are pruned by retention.
+When a sweep applies a system tag but the image ALSO scores highly on a content
+head, it still applies the tag but records this row so a review strip can surface
+it ("⚠ also looks like <conflict tag>"). Two modes (#1464): 'chrome' (banner —
+image is HIDDEN, review is keep-hidden / un-hide) and 'process' (wip / editor
+screenshot — image stays VISIBLE, review is confirm / remove-tag). Resolved rows
+are pruned by retention.
 """
 
 from datetime import datetime
 
-from sqlalchemy import DateTime, Float, ForeignKey, func
+from sqlalchemy import DateTime, Float, ForeignKey, String, func
 from sqlalchemy.orm import Mapped, mapped_column
 
 from .base import Base
@@ -31,6 +33,12 @@ class PresentationReview(Base):
         ForeignKey("tag.id", ondelete="SET NULL"), nullable=True
     )
     conflict_score: Mapped[float] = mapped_column(Float, nullable=False)
+    # Which sweep flagged this (#1464): 'chrome' (banner, hidden) or 'process'
+    # (wip / editor screenshot, shown). Drives which review strip surfaces it and
+    # what "resolve" means (un-hide vs remove-tag). Existing rows backfill 'chrome'.
+    mode: Mapped[str] = mapped_column(
+        String(16), nullable=False, default="chrome", server_default="chrome"
+    )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), nullable=False, server_default=func.now()
     )