Harden Yomitan runtime state and profile policy handling

- Centralize external-profile read-only behavior in a shared Yomitan profile policy
- Clear parser/extension runtime state via dedicated helpers on load failures and reloads
- Prevent opening Yomitan settings when the Yomitan session is unavailable
- Add focused runtime-policy and state-clearing regression tests

changes/external-yomitan-profile.md

@@ -1,6 +1,6 @@
-type: added
+type: changed
 area: config
 
 - Added `yomitan.externalProfilePath` to reuse another Electron app's Yomitan profile in read-only mode.
 - SubMiner now reuses external Yomitan dictionaries/settings without writing back to that profile.
-- Fixed default config bootstrap so `config.jsonc` is seeded even when the config directory already exists.
+- SubMiner now seeds `config.jsonc` even when the default config directory already exists.