feat(dashboardapi): walking skeleton for graph-aware Grafana generator (#34)

Encrypts the Grafana bearer token via Node-RED credentials block instead of
plain config (F-11). Adds folderUid config field threaded through to the
buildUpsertRequest payload (F-8, resolves PRD O-5). Migration path: legacy
plain bearerToken still loads, with one-time warn() prompting user to re-save.

Composition + URL + headers + per-instance UID were already in place; only
the credentials + folderUid + tests are new.

- dashboardAPI.html: bearerToken moved to credentials block; folderUid added.
- dashboardAPI.js: registerType options pass credentials descriptor.
- src/nodeClass.js: read token from node.credentials; legacy fallback warns.
- src/specificClass.js: buildUpsertRequest emits folderUid when set.
- src/commands/handlers.js: pass folderUid from config to buildUpsertRequest.
- test/basic/slice34-credentials-and-folder.basic.test.js: 5 new tests.

Diff-based regeneration (F-1) and the explicit flows:started lifecycle hook
land in #36 once the S1 spike predicate is wired. Until then, the existing
child.register message trigger continues to drive composition on every
startup-time child registration.

Closes #34

src/commands/handlers.js

@@ -48,7 +48,7 @@ function registerChild(source, msg, ctx) {
       headers,
       payload: source.buildUpsertRequest({
         dashboard: dash.dashboard,
-        folderId: 0,
+        folderUid: source.config?.grafanaConnector?.folderUid || undefined,
         overwrite: true,
       }),
       meta: {