feat(sigma): add Sigma Computing context-source adapter (#316)

* feat(sigma): add Sigma Computing context-source adapter

Closes #168

Adds a full ingest adapter for Sigma Computing so `ktx ingest` can pull
data model specs and workbook summaries into the ktx context layer. The
implementation follows the same fetch → chunk → project → LLM pattern
used by the Looker, Metabase, and MetricFlow adapters.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(sigma): address PR review comments

- Remove manifest from rawFiles; moves to peerFileIndex so fetchedAt
  changes don't mark all work units dirty every run
- Fix workbookFilter.updatedSince eviction bug: fetch full universe first,
  apply filter client-side, evict only on archived/deleted
- Remove measure projection entirely; project() writes measures: [] and
  the sigma_ingest skill surfaces Lookup/aggregation formulas as wiki prose
- Remove joins projection (v1 limitation); project() writes joins: [] and
  Lookup relationships are described in wiki prose instead
- Remove write-back dead code: createDataModel, updateDataModel,
  SigmaDataModelPushResult, mutate/post/put
- Fix emitBatches notes pluralization bug ('2 data modelss' → '2 data models')
- Add tokenInflight dedup on ensureToken to coalesce concurrent auth requests
- Retry spec fetch when existing staged spec is null (transient failure cache)
- Drop unused WorkbookFilter import from client-port.ts
- Note in docs that joins are not projected from Sigma data models in this release

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* updates

* fix(sigma): restore sigma in local adapter test + small cleanups

The gdrive↔sigma merge dropped 'sigma' from the expected adapter source
list in local-adapters.test.ts while keeping gdrive, so the slow TS suite
failed even though the source registers both. Add 'sigma' back at its
registration position (after metabase, before gdrive).

Also:
- Move the orphaned SigmaPullConfig docstring onto the schema it documents
  and drop the stale BullMQ reference (standalone ktx has no BullMQ; the
  config lives in the ingest job's bundleRef.config).
- Drop an O(n^2) find() round-trip in fetch() when building the active
  data-model list; filter once and reuse for the eviction id set.

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Andrey Avtomonov <andreybavt@gmail.com>
Co-authored-by: Luca Martial <48870843+luca-martial@users.noreply.github.com>

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

@@ -193,7 +193,7 @@ sources. This is equivalent to passing `--skip-sources` in scripted setup.
 
 | Flag | Description |
 |------|-------------|
-| `--source <type>` | Context-source connector type: `dbt`, `metricflow`, `metabase`, `looker`, `lookml`, or `notion` |
+| `--source <type>` | Context-source connector type: `dbt`, `metricflow`, `metabase`, `looker`, `lookml`, `notion`, or `sigma` |
 | `--source-connection-id <id>` | Connection id for context-source setup |
 | `--source-path <path>` | Local source path for dbt, MetricFlow, or LookML |
 | `--source-git-url <url>` | Git URL for dbt, MetricFlow, or LookML |
@@ -278,6 +278,13 @@ ktx setup \
   --notion-crawl-mode selected_roots \
   --notion-root-page-id abc123def456
 
+# Add a Sigma source
+ktx setup \
+  --source sigma \
+  --source-connection-id sigma-main \
+  --source-client-id your-client-id \
+  --source-client-secret-ref env:SIGMA_CLIENT_SECRET
+
 # Install project-scoped agent integration for Codex
 ktx setup --agents --target codex
 ```