feat(dashboardapi): manual regen via msg.topic == regenerate-dashboard (#41)

Adds an explicit topic for operators (and the dashboardAPI v2 manual escape
hatch from PRD F-12). On `regenerate-dashboard`, dashboardAPI iterates every
child source cached by prior `child.register` messages and re-emits Grafana
upsert messages — bypassing the diff-skip predicate from #36.

- src/specificClass.js: light state cache (recordChild / cachedChildSources).
- src/commands/handlers.js: refactor shared emit path; emitDashboardsFor()
  used by both child.register and regenerateDashboard; meta.trigger
  distinguishes the two for downstream filtering.
- src/commands/index.js: register 'regenerate-dashboard' (alias 'regen').
- CONTRACT.md: document the new topic.
- test/basic/slice41-manual-regen.basic.test.js: 5 cases covering cache
  semantics, no-op for empty cache, bypass-predicate, trigger stamp on both
  paths, registry exposure.

Closes #41

src/commands/index.js

@@ -13,4 +13,10 @@ module.exports = [
     payloadSchema: { type: 'any' },
     handler: handlers.registerChild,
   },
+  {
+    topic: 'regenerate-dashboard',
+    aliases: ['regen'],
+    payloadSchema: { type: 'any' },
+    handler: handlers.regenerateDashboard,
+  },
 ];