feat(session-title): user rename pins the title against automatic generation

sessionTitle.rename appends a user-source session/title event; onUserMessage
skips scheduling while a user title stands, and an explicit refresh is the
deliberate unpin (provider regeneration, or a re-derived fallback when no
provider is registered).

docs/core-data-structures/session-title.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write docs/core-data-structures/session-title.md
-session-title.md: 33efc911c0ca1ae94dc4ded74676e5c32a73bdd5
-session-title.zh.md: a4b95a726d2bc89a13d14f1daa2f825cd5aa91b1
+session-title.md: 0857f5255be616d00ea1f49fdfd97cffda1fd4b2
+session-title.zh.md: 75fa42bfbdec18afc20ca59e2c02631e01cfd994

docs/core-data-structures/session-title.md

@@ -34,6 +34,10 @@ type SessionTitleSource =
     readonly provider: SessionTitleProviderId
     readonly model?: SessionTitleModelProvenance
   }
+  | {
+    /** Explicit user rename: pins the title — automatic generation stops scheduling. */
+    readonly kind: 'user'
+  }
 ```
 
 ```ts type-equiv

docs/core-data-structures/session-title.zh.md

@@ -34,6 +34,10 @@ type SessionTitleSource =
     readonly provider: SessionTitleProviderId
     readonly model?: SessionTitleModelProvenance
   }
+  | {
+    /** Explicit user rename: pins the title — automatic generation stops scheduling. */
+    readonly kind: 'user'
+  }
 ```
 
 ```ts type-equiv