refactor(subtitles): introduce SubtitleKnowledge Protocol port

Domain services (SubtitleIdentifier, PatternDetector) used to import the
concrete SubtitleKnowledgeBase class directly from infrastructure for
their type hint. With this commit they depend on a structural Protocol
in alfred/domain/subtitles/ports/knowledge.py declaring just the 7
read-only query methods the domain actually consumes.

The concrete YAML-backed SubtitleKnowledgeBase in infrastructure remains
the sole adapter — no rename, no shim. With this change
alfred/domain/subtitles/ has zero imports from alfred/infrastructure/.

Also extend the changelog entry covering the full domain-io-extraction
branch.

CHANGELOG.md

@@ -143,6 +143,17 @@ callers).
     an explicit `default_rules: SubtitleMatchingRules` parameter. The
     `ManageSubtitles` use case loads defaults from the KB once and
     passes them in.
+  - **`SubtitleKnowledge` Protocol port** at
+    `alfred/domain/subtitles/ports/knowledge.py` declares the read-only
+    query surface domain services consume (7 methods:
+    `known_extensions`, `format_for_extension`, `language_for_token`,
+    `is_known_lang_token`, `type_for_token`, `is_known_type_token`,
+    `patterns`). `SubtitleIdentifier` and `PatternDetector` depend on
+    this Protocol instead of the concrete `SubtitleKnowledgeBase` from
+    infrastructure — `domain/subtitles/` now has zero imports from
+    `infrastructure/`. The remaining domain → infra leak
+    (`domain/release/` loading separator YAML at import-time) is
+    documented in tech-debt and scheduled for its own branch.
 - **`to_dot_folder_name(title)` helper** in
   `alfred/domain/shared/value_objects.py` — extracts the
   `re.sub(r"[^\w\s\.\-]", "", title).replace(" ", ".")` pattern that was