chore: cleanup — remove shims, fix ruff warnings, ignore noisy rules

- Removed backward-compat shims _sanitise_for_fs / _strip_episode_from_normalised
  in domain/release/value_objects.py (zero callers).
- Fixed ruff warnings across the codebase:
    * PLW1510: explicit check=False on subprocess.run calls
    * PLC0415: promoted lazy imports to module top where no cycle exists
      (manage_subtitles, placer, qbittorrent/client, file_manager)
    * E402: fixed module-level import ordering in language_registry.py and
      subtitles/knowledge/loader.py
    * F841 / B007: removed unused locals (identifier.py)
    * C416: replaced unnecessary set comprehension with set() in
      release/knowledge.py
- Ruff config: ignore PLR0911/PLR0912 globally (noisy on mappers and
  orchestrator use-cases) and PLW0603 (intentional for the memory singleton).
- Updated tech debt memory: P1 done, ShowStatus actually complete (was a
  stale note).

pyproject.toml

@@ -136,7 +136,15 @@ lint.select = [
     "PL",
     "UP",
 ]
-lint.ignore = ["PLR0913", "PLR2004", "TID252", "E501"]
+lint.ignore = [
+    "PLR0911",  # too-many-returns: noisy on mappers / orchestrator use-cases with early-return validation
+    "PLR0912",  # too-many-branches: same as above
+    "PLR0913",  # too-many-arguments
+    "PLR2004",  # magic-value-comparison
+    "PLW0603",  # global statement: intentional for the memory singleton (see project_memory_singleton.md)
+    "TID252",
+    "E501",
+]
 
 [tool.ruff.lint.per-file-ignores]
 "tests/**/*.py" = ["PLC0415"]