refactor: test row factories and the fetch stub have one copy each (3109)

tests/factories.py holds image_row/make_image/make_image_async/make_tag. The
17 byte-identical _img/_tag helpers (15 modules) now import them under their
old names, so no call site changed. frontend/test/support/stubFetch.js
replaces 15 copies that differed only in formatting. Copies whose bodies
differ (other defaults, other columns, a url-only stub) are left as they
are; folding those needs a look at each caller.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

tests/factories.py

@@ -0,0 +1,47 @@
+"""Throwaway rows for tests: one copy of the placeholder columns (#3109).
+
+`ImageRecord` needs a unique path and sha256 plus six NOT NULL columns no test
+cares about. Fifteen modules re-typed the same builder, so a new NOT NULL column
+meant fifteen separate patches. The tests that need these rows import them from
+here, usually under their old local name (`make_image as _img`), so their call
+sites did not change.
+"""
+
+from backend.app.models import ImageRecord, Tag, TagKind
+
+
+def image_row(sha: str, emb=None, **overrides) -> ImageRecord:
+    """An unsaved ImageRecord keyed by `sha`; `emb` is its SigLIP embedding."""
+    fields = {
+        "path": f"/images/{sha}.jpg", "sha256": sha, "size_bytes": 1,
+        "mime": "image/jpeg", "width": 1, "height": 1,
+        "origin": "imported_filesystem", "integrity_status": "unknown",
+    }
+    if emb is not None:
+        fields["siglip_embedding"] = emb
+    fields.update(overrides)
+    return ImageRecord(**fields)
+
+
+def make_image(db, sha: str, emb=None, **overrides) -> ImageRecord:
+    """image_row, added and flushed on a sync session."""
+    img = image_row(sha, emb, **overrides)
+    db.add(img)
+    db.flush()
+    return img
+
+
+async def make_image_async(db, sha: str, emb=None, **overrides) -> ImageRecord:
+    """image_row, added and flushed on an async session."""
+    img = image_row(sha, emb, **overrides)
+    db.add(img)
+    await db.flush()
+    return img
+
+
+def make_tag(db, name: str, **overrides) -> Tag:
+    """A general tag, added and flushed on a sync session."""
+    tag = Tag(**{"name": name, "kind": TagKind.general, **overrides})
+    db.add(tag)
+    db.flush()
+    return tag