refactor(shared): deduplicate model resolution utility functions

Extract normalizeModel() (3 identical copies) and normalizeModelID()
(2 identical copies) into canonical src/shared/model-normalization.ts.
Delete dead-end duplicate model-name-matcher.ts. Update all consumers.

src/shared/fallback-model-availability.ts

@@ -1,6 +1,6 @@
 import { readConnectedProvidersCache } from "./connected-providers-cache"
 import { log } from "./logger"
-import { fuzzyMatchModel } from "./model-name-matcher"
+import { fuzzyMatchModel } from "./model-availability"
 
 type FallbackEntry = { providers: string[]; model: string }