Add configuration source reports

docs/cli.md

@@ -147,6 +147,32 @@ one comment line. A provider failure leaves the output stream empty. A rendering
 or output failure may leave an aggregate prefix, and the outcome reports
 incomplete report delivery.
 
+### List configuration sources
+
+`config sources` reports the source inventory captured during the selected
+scope's acquisition. It reads the source facet once and does not reload
+configuration. The default scope is `app`; `--scope all` is unsupported. Text is
+the default format, and `--format yaml` returns a structured report:
+
+```yaml
+scope: app
+sources:
+  - id: source-1
+    label: "application config"
+    path: /etc/example/config.yml
+    layer: base
+    kind: file
+    underlay_index: 0
+    imported_from: null
+```
+
+Each source includes `id`, `label`, `path`, `layer`, `kind`, `underlay_index`,
+and `imported_from`. The import location is null when absent; otherwise it has
+`source_id`, `line`, and `column`. Owning values and source order are preserved,
+including empty fields, zero coordinates, and synthetic sources without paths.
+An empty inventory is `sources: []`. Text output begins with the scope heading
+and then prints the same source fields, quoting labels and paths.
+
 ## Outcome status
 
 CommandKit usage failures use status `2`; operational failures use status `1`.