refactor(context): validate ktx.yaml with Zod and surface issues in status (#91)

* refactor(context): validate ktx.yaml with Zod and surface issues in status

- Replace hand-rolled ktx.yaml parsing with a strict Zod schema and
  derive KtxProjectConfig types from it.
- Add validateKtxProjectConfig returning structured KtxConfigIssue[]
  with migration hints for deprecated keys (ingest.llm,
  scan.enrichment.backend, etc.).
- Wire ktx status/doctor to run validation, render schema issues in
  plain and JSON output, and add a Config row to project status.
- Update the orbit example to camelCase scan.relationships keys to
  match the schema.

* fix(context): tolerate legacy setup.completed_steps and optional driver

- Accept and drop the legacy setup.completed_steps field so existing
  ktx.yaml files migrated from older versions still load.
- Make connections.<id>.driver optional in the schema; runtime code
  already produces a clear "no driver" error at use time.

* feat(cli): add ktx status --validate to run only ktx.yaml schema validation

- New --validate flag dispatches a focused runKtxDoctor 'validate' branch
  that reads ktx.yaml, runs validateKtxProjectConfig, and skips LLM,
  connection, embedding, and query-history checks.
- Plain output prints a single Config row; JSON output emits
  {ok: true} on success or the existing invalid_config / missing_project
  shapes on failure.

packages/context/src/project/index.ts

@@ -1,4 +1,6 @@
 export type {
+  KtxConfigIssue,
+  KtxConfigValidation,
   KtxProjectConfig,
   KtxProjectConnectionConfig,
   KtxProjectEmbeddingConfig,
@@ -10,6 +12,7 @@ export {
   buildDefaultKtxProjectConfig,
   parseKtxProjectConfig,
   serializeKtxProjectConfig,
+  validateKtxProjectConfig,
 } from './config.js';
 export type { LocalGitFileStoreDeps } from './local-git-file-store.js';
 export { LocalGitFileStore } from './local-git-file-store.js';