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.

examples/orbit-relationship-verification/ktx.yaml

@@ -13,14 +13,14 @@ ingest:
   adapters: []
 scan:
   enrichment:
-    backend: none
+    mode: none
   relationships:
     enabled: true
-    llm_proposals: false
-    validation_required_for_manifest: true
-    accept_threshold: 0.85
-    review_threshold: 0.55
-    max_llm_tables_per_batch: 40
-    max_candidates_per_column: 25
-    profile_sample_rows: 10000
-    validation_concurrency: 4
+    llmProposals: false
+    validationRequiredForManifest: true
+    acceptThreshold: 0.85
+    reviewThreshold: 0.55
+    maxLlmTablesPerBatch: 40
+    maxCandidatesPerColumn: 25
+    profileSampleRows: 10000
+    validationConcurrency: 4