feat(cli): consistent connection setup recovery and build-time gate (#257)

* feat(cli): block context build when a required connection fails its live test

A context build can take several minutes, so a connection that is
unreachable or misconfigured should stop the build up front instead of
failing partway through. Before the build starts, run a live connection
test for every primary- and context-source connection the build depends
on.

Each test's output is captured in a discarded buffer so raw error text
(and database paths) never reach the user; failures are surfaced only by
connection id and connector type, with a pointer to `ktx connection test
<id>` for the underlying error.

- Interactive setup lets the user fix the connection and retry without
  restarting, re-resolving targets so an added/removed/reconfigured
  connection is honored.
- `--no-input` exits non-zero and writes a failed context state with a
  failureReason, so scripts stop early and setup never reads as ready.

Extract the buffered command IO helper out of setup-databases into
src/io/buffered-command-io.ts so both call sites share one implementation.

* feat(cli): use recovery primitive for database setup

* feat(cli): use recovery primitive for source setup

* docs: document setup connection recovery

* fix(cli): close database recovery gaps

* fix(cli): target failing project in gate hint and preserve missing-input

Address two review findings on the connection-recovery work:

- The connection-gate failure hint emitted `ktx connection test <id>` with no
  --project-dir, so a setup run started with `--project-dir ./analytics` pointed
  users at cwd/KTX_PROJECT_DIR instead of the project that just failed. Emit the
  resolved project dir, matching the contextBuildCommands convention.

- The non-interactive database configure path returned `cancelled`, which the
  recovery primitive collapses to `failed`. Sibling paths still report
  `missing-input` for absent flags, so incomplete-flag runs were
  indistinguishable from real connection failures. The database wrapper now
  tracks the configure missing-input signal and restores the `missing-input`
  step status; the shared primitive keeps its four outcomes.

docs-site/content/docs/cli-reference/ktx-connection.mdx

@@ -104,6 +104,6 @@ configured connection and exit non-zero if any probe fails.
 | Error | Cause | Recovery |
 |-------|-------|----------|
 | No connections configured | The project has no entries under `connections` | Run `ktx setup` and add a database or context-source connection |
-| Connection test fails | Credentials, network access, database, warehouse, or schema is invalid | Verify the same URL with the database's native client, then rerun `ktx setup` and reconfigure the connection |
-| Mapping validation fails during setup | BI database mappings do not point at valid warehouse connections | Rerun `ktx setup` and update the context-source mapping selections |
+| Connection test fails | Credentials, network access, database, warehouse, or schema is invalid | Use the setup recovery menu to retry or re-enter details; if it still fails, verify the same URL with the database's native client |
+| Mapping validation fails during setup | BI database mappings do not point at valid warehouse connections | Use the setup recovery menu to retry validation or re-enter mapping selections; rerun `ktx setup` if you already exited |
 | Notion page picker cannot run | The terminal is non-interactive or Notion discovery failed | Rerun interactive `ktx setup`, or use non-interactive setup flags with explicit root page ids |