feat(cli)!: remove fast mode; ktx ingest always builds enriched context (KLO-721)

Fast mode (the ktx ingest --fast/--deep database-ingest depth toggle) is removed.
ktx ingest now always builds the full enriched ("deep") context. There is no
structural fallback: a database connection without a configured model and
embeddings fails the enrichment-readiness preflight before any work runs, with
a 'Run ktx setup to configure a model and embeddings' hint.

- Remove --fast/--deep flags, the per-connection context.depth field, and the
  ktx setup depth prompt (delete setup-database-context-depth.ts).
- Rename ingest-depth.ts -> connection-drivers.ts; ingest always requests scan
  mode 'enriched'; readiness gate (enrichmentReadinessGaps) runs for every
  database target.
- Drop the database-context-depth telemetry step (Node + Python schema mirrors
  regenerated).
- Update CLI, setup, context-build view, docs, the public ktx skill, and the
  release-smoke / artifacts scripts (now assert the no-LLM guard failure).

ktx status --fast (a separate network-probe flag) is unchanged.

Follow-ups: KLO-726 (live progress for ktx ingest --all), KLO-727 (restore
credentialed successful-ingest release smoke coverage).

docs-site/content/docs/getting-started/quickstart.mdx

@@ -236,7 +236,7 @@ Testing warehouse
   Connection test passed
 
 Building schema context for warehouse
-  Running fast database ingest
+  Running database scan
 ```
 
 If setup exits early, rerun `ktx setup` in the same directory. **ktx** keeps
@@ -268,13 +268,13 @@ Agent integration ready: yes (codex:project)
 
 For a structured check inside scripts, use `ktx status --json`.
 
-When setup builds deep context, its final context check looks like:
+When setup finishes building context, its final context check looks like:
 
 ```text
 ktx context is ready for agents.
 
 Databases:
-  warehouse: deep context complete
+  warehouse: database context complete
 
 Context sources:
   dbt_main: memory update complete
@@ -326,7 +326,7 @@ ktx setup \
 Then build context:
 
 ```bash
-ktx ingest warehouse --fast
+ktx ingest warehouse
 ```
 
 See [ktx setup](/docs/cli-reference/ktx-setup) for the full automation flag