fix(kernel,router): rehydrate by CAS content hash (F-021) + narration budget

rehydrate() now scans ArtifactContentStoredEvent (the durable slot->CAS-hash
bridge) and fetches stored bytes by content hash, keying the cache by the
logical slot name. The slot name is never passed to the hash-keyed CAS, so the
odd-length-hex crash is gone and artifact content is restored on cold-start
resume. RehydrateTest reworked to use a content-addressed fake store (slot name
!= content hash) so it actually exercises the bug. Replay (#8) is unaffected —
rehydrate is live-resume-only.

Also bump router narration maxTokens 1024 -> 4096: reasoning models were
spending the whole budget thinking and emitting empty content (finishReason=
length), so narrations never reached the TUI.

Removes the stale TUI-refactor progress doc.

core/router/src/main/kotlin/com/correx/core/router/model/RouterConfig.kt

@@ -15,12 +15,13 @@ data class RouterConfig(
         maxTokens = 512,
     ),
     // Narration uses a larger token ceiling: reasoning models spend tokens "thinking"
-    // before emitting content, and a 512 cap left no room for the actual line (the
-    // response came back empty with finishReason=length). 1024 lets thinking complete
-    // and still produce the one or two sentences.
+    // before emitting content, and a tighter cap left no room for the actual line (the
+    // response came back empty with finishReason=length). 1024 still wasn't enough —
+    // the model burned the whole budget reasoning and emitted no content — so 4096
+    // gives reasoning room to complete and still produce the one or two sentences.
     val narrationGenerationConfig: GenerationConfig = GenerationConfig(
         temperature = 0.7,
         topP = 0.9,
-        maxTokens = 1024,
+        maxTokens = 4096,
     ),
 )