feat: code-intelligence contract with real GBrain/Graphify/Sourcebot adapters

contract.ts: repo-oriented interface (four required ops, three optional),
typed CodeProviderError, egress + capability consent guards.

Three real, runtime-drivable adapters:
- GbrainProvider: gbrain CLI (reuses lib/gbrain-exec + lib/gbrain-sources),
  all seven capabilities.
- GraphifyProvider: graphify CLI — `graphify <dir>` builds the local graph,
  `graphify query` searches it, export reads graphify-out/graph.json. Fully
  local; never auto-installed.
- SourcebotProvider: self-hosted server over HTTP — register writes a local
  git connection to config.json, search is POST /api/search, status is a
  liveness probe. Loopback base URL = local (no egress); remote = consent.

selection.ts persists the chosen provider + per-repo indexing consent under
$GSTACK_HOME. picker.ts recommends GBrain first, resolves the selected
provider or null (provider-OFF), and probes live availability. Every adapter
degrades to PROVIDER_UNAVAILABLE when its tool/server is absent.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/code-intelligence/index.ts

@@ -5,10 +5,20 @@
 
 export * from "./contract";
 export { GbrainProvider, parseGbrainSearch } from "./gbrain-adapter";
-export { SourcebotProvider, GraphifyProvider } from "./mcp-adapters";
+export { GraphifyProvider, parseGraphifyQuery, type GraphifyOptions } from "./graphify-adapter";
+export { SourcebotProvider, parseSourcebotSearch, type SourcebotOptions } from "./sourcebot-adapter";
+export {
+  readSelection,
+  setProvider,
+  setConsent,
+  hasConsent,
+  type Selection,
+} from "./selection";
 export {
-  recommendCodeProvider,
-  resolveCodeProvider,
   RECOMMENDED_ORDER,
+  providerById,
+  resolveSelectedProvider,
+  detectAvailable,
   type PickerOptions,
+  type Availability,
 } from "./picker";