feat(release): pre-pipeline exclusion helpers

Add the application-layer helpers that decide which files are worth
parsing, sitting one notch above parse_release.

- is_supported_video(path, kb): extension-only check against
  kb.video_extensions. Lowercased suffix lookup. Directories and
  broken symlinks return False.
- find_main_video(folder, kb): top-level scan only (no recursion into
  subdirectories — releases that wrap their video in Sample/ are
  PATH_OF_PAIN territory). Lexicographically-first eligible file wins
  when several qualify (deterministic, no size-based ranking). A bare
  file as folder argument is supported for single-file releases.

No size threshold and no filename heuristics ('sample' / 'trailer'):
the parser's job is to extract structure, not to second-guess
non-standard release shapes. PoP catches the rest.

17 tests under tests/application/test_supported_media.py.

CHANGELOG.md

@@ -17,6 +17,15 @@ callers).
 
 ### Added
 
+- **Pre-pipeline exclusion helpers** (`alfred/application/release/supported_media.py`):
+  `is_supported_video(path, kb)` (extension-only check against
+  `kb.video_extensions`) and `find_main_video(folder, kb)` (top-level
+  scan, lexicographically-first eligible file, returns `None` when no
+  video qualifies; accepts a bare file as folder for single-file
+  releases). No size threshold, no filename heuristics —
+  PATH_OF_PAIN handles the exotic cases. Foundation for the future
+  `inspect_release` orchestrator.
+
 - **Release parser — parse-confidence scoring** (`alfred/domain/release/parser/scoring.py`,
   `alfred/knowledge/release/scoring.yaml`). `parse_release` now returns
   `(ParsedRelease, ParseReport)`. The new `ParseReport` frozen VO