Slice 3 wave A: tabs model, model selector, cache delete, localStorage

- features/tabs: pure tab-workspace reducer (create/select/close/setModel/
  setTitle/deriveTitle, draft=null active) + injected-persistence runes store
- features/chat: mutable per-tab model (setModel) + delta routing guard
  (ignore foreign conversationId) + ModelSelector.svelte + DaisyUI chat bubbles
  / composer (keeps streaming <details> keying fix)
- features/conversation-cache: surface delete(conversationId) on the wrapper
  for tab-close local-forget
- adapters/local-storage: generic injected JSON localStore<T> (quota/corrupt-safe)

Verified: svelte-check 0/0, vitest 273, biome clean, build ok.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/features/conversation-cache/cache.ts b/src/features/conversation-cache/cache.ts
index 4aab487..3d5743a 100644
--- a/src/features/conversation-cache/cache.ts
+++ b/src/features/conversation-cache/cache.ts
@@ -20,6 +20,9 @@ export interface ConversationCache {
 	 * Returns the evicted conversationIds.
 	 */
 	evictIfOverBudget(activeConversationId: string | null): Promise<readonly string[]>;
+
+	/** Delete all cached data for a single conversation (local forget). */
+	delete(conversationId: string): Promise<void>;
 }
 
 export interface ConversationCacheOptions {
@@ -67,5 +70,9 @@ export function createConversationCache(
 			}
 			return toEvict;
 		},
+
+		async delete(conversationId) {
+			await store.delete(conversationId);
+		},
 	};
 }