refactor(model-core): host snapshot fetcher, suggestion parser, and context-limit resolver

Move three pure helpers from src/shared/ into @oh-my-opencode/model-core so the package can stand alone without depending on plugin internals:

- buildModelCapabilitiesSnapshotFromModelsDev + fetchModelCapabilitiesSnapshot (models.dev normalization)
- parseModelSuggestion (cross-provider ProviderModelNotFoundError suggestion extraction)
- resolveActualContextLimit (Anthropic GA 1M context override)

Split provider-model-id-transform into two variants exposed by model-core:

- transformModelForProvider keeps the runtime dash to dot Anthropic rewrite used by the SDK
- transformModelForProviderDisplay preserves hyphenated Anthropic IDs so the installer writes registry-compatible model strings, fixing the ProviderModelNotFoundError fresh installs hit when the dotted form leaks into the config

src/shared/* and src/cli/provider-model-id-transform.ts collapse to re-export shims that point at the new core modules. Stale src/shared/{known-variants,model-capability-aliases,model-capability-guardrails,model-capability-heuristics}.ts re-export files plus the duplicated context-limit-resolver test are removed in favor of the canonical model-core copies.

Tests: bun test packages/model-core src/shared/model-capabilities-cache.test.ts src/cli/provider-model-id-transform.test.ts

src/shared/index.ts

@@ -48,7 +48,6 @@ export type {
 export * from "./model-availability"
 export * from "./model-capabilities"
 export * from "./model-capabilities-cache"
-export * from "./model-capability-heuristics"
 export * from "./model-settings-compatibility"
 export * from "./fallback-model-availability"
 export * from "./connected-providers-cache"