feat(gallery): default-hide presentation chrome (banner/editor screenshot) (#141 step 1)

The default gallery + facets now implicitly exclude images carrying a
presentation system tag (banner / editor screenshot), reusing the tag-scope
EXISTS machinery. Suppressed when the operator explicitly filters FOR a
presentation tag OR passes include_hidden (the Hidden view — step 2). `wip` is
NOT hidden (real, in-progress art). include_hidden threaded through
scroll/timeline/jump_cursor/facets + the gallery API _parse_filters. Test covers
default-hide, include_hidden, explicit-filter-shows, and wip-stays-visible.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

tests/test_gallery_service.py

@@ -1,6 +1,7 @@
 from datetime import UTC, datetime, timedelta
 
 import pytest
+from sqlalchemy import select
 
 from backend.app.models import ImageRecord, Tag, TagKind
 from backend.app.models.tag import image_tag
@@ -73,6 +74,47 @@ async def test_scroll_returns_newest_first(db):
     assert page.images[0].created_at > page.images[-1].created_at
 
 
+async def _system_tag(db, name):
+    return (await db.execute(
+        select(Tag).where(Tag.is_system.is_(True), Tag.name == name)
+    )).scalar_one()
+
+
+@pytest.mark.asyncio
+async def test_scroll_hides_presentation_chrome_by_default(db):
+    # banner / editor screenshot (presentation system tags) are hidden from the
+    # default gallery; wip (also a system tag) is NOT — it's real, in-progress
+    # art (milestone 141). Seeded system tags survive the harness TRUNCATE.
+    imgs = await _seed_images(db, 3, sha_prefix="p")
+    banner = await _system_tag(db, "banner")
+    wip = await _system_tag(db, "wip")
+    await db.execute(image_tag.insert().values(
+        image_record_id=imgs[0].id, tag_id=banner.id, source="manual"))
+    await db.execute(image_tag.insert().values(
+        image_record_id=imgs[1].id, tag_id=wip.id, source="manual"))
+    await db.flush()
+    svc = GalleryService(db)
+
+    # Default: the banner image is hidden; the wip image + the plain image stay.
+    default_ids = {i.id for i in (await svc.scroll(cursor=None, limit=10)).images}
+    assert imgs[0].id not in default_ids      # banner hidden
+    assert imgs[1].id in default_ids          # wip visible
+    assert imgs[2].id in default_ids          # plain visible
+
+    # include_hidden surfaces the banner image (the Hidden view).
+    shown = {i.id for i in (
+        await svc.scroll(cursor=None, limit=10, include_hidden=True)
+    ).images}
+    assert imgs[0].id in shown
+
+    # Filtering explicitly FOR banner shows it (a view exclusively for a
+    # presentation tag suppresses the implicit hide).
+    only_banner = {i.id for i in (
+        await svc.scroll(cursor=None, limit=10, tag_ids=[banner.id])
+    ).images}
+    assert only_banner == {imgs[0].id}
+
+
 @pytest.mark.asyncio
 async def test_scroll_sorts_by_earliest_post_date(db):
     """posted_new/posted_old key off earliest_post_date (original publish across