repos: backend — schema, /api/repos routes + GitHub sync provider

Migration 0034: two tables. repo_connections carries the workspace's
per-provider config (owner, base_url, label, last_synced_at,
last_sync_error) and points at an app_connections row for the PAT.
repos is the per-connection cache with (connection_id, external_id)
unique so upsert is idempotent across re-syncs. Cascading deletes clean
up cleanly on connection removal.

cm-secrets grows a FetchAuthorized op — GET with the stored PAT injected
as bearer, returns status + JSON body without ever exposing the
credential to cm-api. This is the least-privilege door for read-only
provider APIs (list repos), distinct from the InvokeHttp path that still
requires a single-use approval grant for outbound writes.

cm-api::routes::repos wires:
- POST /api/repos/connections (broker store_secret + insert both rows +
  initial sync + mark_synced)
- GET /api/repos/connections
- DELETE /api/repos/connections/:id
- POST /api/repos/connections/:id/sync
- GET /api/repos (500 cap, newest provider_updated first)
- GET /api/repos/:id (full detail incl. clone_url + html_url)

GitHub provider inline for v1 — paginated pull of /orgs/:owner/repos
(when owner set) or /user/repos (when absent), 100/page, capped at 20
pages (~2k repos) to keep first-sync latency bounded. Non-2xx surface
back to the caller as sync_error; parse failures are best-effort per
repo (skipped, logged, don't abort the batch).

Gitea + GitLab providers land in a follow-up — mostly URL swap +
response-shape adapter.

.sqlx/query-ecff5e7cad6960b7da3daaba89f46d2b0ce1554d78b2ea34d14b5137f7b5ee67.json

@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "DELETE FROM repos WHERE connection_id = $1 AND workspace_id = $2",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "ecff5e7cad6960b7da3daaba89f46d2b0ce1554d78b2ea34d14b5137f7b5ee67"
+}