fix(downloads): a download larger than the space left says so, not "processing failed"

yt-dlp refuses a file announced over `max_filesize` by logging one line and returning with no file
(measured, and pinned in test_formats against a local server): the worker found no output and
failed the job as `postprocess`. `formats.watching_size_cap` now sees that line through our yt-dlp
logger, and the download (and, should it ever happen, a YouTube clip's range fetch) fails as the
owner's refusal with DOWNLOAD_TOO_BIG_MESSAGE, classified `quota_exceeded`. The download's quota
copy says it does not fit in what is left — true at a full cap too — instead of "Storage full".
A pre-existing type error the change touched is fixed (baseline down by one).

backend/.basedpyright/baseline.json

@@ -437,14 +437,6 @@
                     "lineCount": 1
                 }
             },
-            {
-                "code": "reportArgumentType",
-                "range": {
-                    "startColumn": 12,
-                    "endColumn": 13,
-                    "lineCount": 10
-                }
-            },
             {
                 "code": "reportAttributeAccessIssue",
                 "range": {