feat(gallery): tag→gallery nav from modal chips (#5) + OR/exclude tag scope (#6a)

Cluster A, milestone #97. #5: clicking an image-modal tag chip's body now
closes the modal and opens the gallery filtered for that one tag (fresh
filter); ✕/kebab stay as the explicit remove/rename controls.

#6a (backend of OR/exclude filtering): gallery_service._apply_scope gains a
structured tag model — tag_or_groups (AND-of-OR: one EXISTS(tag_id IN group)
per group) + tag_exclude (NOT EXISTS(tag_id IN exclude)) — layered additively
on the existing tag_ids AND path so cursors/facets/deep-links are untouched.
Threaded through scroll/timeline/jump_cursor/facets/similar + facets common
dict; _require_single_filter rejects post_id combined with OR/exclude. API
parses tag_or (repeatable → one OR-group each) + tag_not (csv exclude).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XCUHUGQLrBrkgyk1t49kpX

tests/test_api_gallery.py

@@ -2,7 +2,8 @@ from datetime import UTC, datetime, timedelta
 
 import pytest
 
-from backend.app.models import ImageRecord
+from backend.app.models import ImageRecord, Tag, TagKind
+from backend.app.models.tag import image_tag
 
 pytestmark = pytest.mark.integration
 
@@ -114,3 +115,62 @@ async def test_scroll_date_from_param(client, db):
     resp = await client.get("/api/gallery/scroll?date_from=2099-01-01&limit=10")
     assert resp.status_code == 200
     assert (await resp.get_json())["images"] == []
+
+
+async def _seed_tagged(db):
+    """3 images: [0]→a, [1]→b, [2]→x. Returns (records, {a,b,x} tag ids)."""
+    records = []
+    base = datetime.now(UTC)
+    for i in range(3):
+        r = ImageRecord(
+            path=f"/images/t/{i}.jpg", sha256=f"t{i:063d}",
+            size_bytes=1, mime="image/jpeg", width=1, height=1,
+            origin="imported_filesystem", integrity_status="unknown",
+        )
+        r.created_at = base - timedelta(minutes=i)
+        r.effective_date = r.created_at
+        db.add(r)
+        records.append(r)
+    a = Tag(name="apia", kind=TagKind.general)
+    b = Tag(name="apib", kind=TagKind.general)
+    x = Tag(name="apix", kind=TagKind.general)
+    db.add_all([a, b, x])
+    await db.flush()
+    await db.execute(image_tag.insert().values([
+        {"image_record_id": records[0].id, "tag_id": a.id, "source": "manual"},
+        {"image_record_id": records[1].id, "tag_id": b.id, "source": "manual"},
+        {"image_record_id": records[2].id, "tag_id": x.id, "source": "manual"},
+    ]))
+    await db.commit()
+    return records, {"a": a.id, "b": b.id, "x": x.id}
+
+
+@pytest.mark.asyncio
+async def test_scroll_tag_or_param(client, db):
+    # ?tag_or=a,b is one OR-group → images carrying a OR b (not x-only).
+    records, ids = await _seed_tagged(db)
+    resp = await client.get(f"/api/gallery/scroll?tag_or={ids['a']},{ids['b']}&limit=10")
+    assert resp.status_code == 200
+    got = {i["id"] for i in (await resp.get_json())["images"]}
+    assert got == {records[0].id, records[1].id}
+
+
+@pytest.mark.asyncio
+async def test_scroll_tag_not_param(client, db):
+    # ?tag_not=x excludes the x-tagged image.
+    records, ids = await _seed_tagged(db)
+    resp = await client.get(f"/api/gallery/scroll?tag_not={ids['x']}&limit=10")
+    assert resp.status_code == 200
+    got = {i["id"] for i in (await resp.get_json())["images"]}
+    assert got == {records[0].id, records[1].id}
+
+
+@pytest.mark.asyncio
+async def test_scroll_repeated_tag_or_groups_anded(client, db):
+    # Two ?tag_or= groups AND together: (a) AND (b) → no single image has both.
+    records, ids = await _seed_tagged(db)
+    resp = await client.get(
+        f"/api/gallery/scroll?tag_or={ids['a']}&tag_or={ids['b']}&limit=10"
+    )
+    assert resp.status_code == 200
+    assert (await resp.get_json())["images"] == []