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, 3 insertions, 0 deletions

diff --git a/src/features/chat/test-helpers.ts b/src/features/chat/test-helpers.ts
index e58818a..d37b59e 100644
--- a/src/features/chat/test-helpers.ts
+++ b/src/features/chat/test-helpers.ts
@@ -75,6 +75,9 @@ export function createFakeCache(): FakeCache {
 			async evictIfOverBudget() {
 				return [];
 			},
+			async delete(conversationId) {
+				store.delete(conversationId);
+			},
 		},
 	};
 }