Gallery: match image endpoint URLs with exact v1 suffix

The image-edit endpoint lookup compared stored vs incoming base URLs with
`.rstrip("/v1")`. `str.rstrip(chars)` treats its argument as a character
set, not a suffix, so any URL ending in '/', 'v', or '1' is over-stripped
(e.g. `http://host1/v1` -> `http://host`). Two endpoints that are not the
same can then compare equal, or the real endpoint fails to match its own
stored record, leaving `api_key` unset and sending the upstream image call
unauthenticated.

Use `.removesuffix("/v1")` (exact-suffix removal) with surrounding
`.rstrip("/")` on both sides so only a genuine trailing `/v1` is dropped.

Adds a focused test that parses the actual comparison expression out of
gallery_routes.py via AST and evaluates it — it fails if the fix is
reverted and uses no mocking.

routes/gallery_routes.py

@@ -1136,7 +1136,7 @@ def setup_gallery_routes() -> APIRouter:
             db = SessionLocal()
             try:
                 for ep in db.query(ModelEndpoint).all():
-                    if ep.base_url.rstrip("/").rstrip("/v1") == base.rstrip("/v1"):
+                    if ep.base_url.rstrip("/").removesuffix("/v1").rstrip("/") == base.rstrip("/").removesuffix("/v1").rstrip("/"):
                         api_key = ep.api_key
                         break
             finally: