feat(dashboardapi): emittedFields metadata for parent-panel dedup (#37)

Adds per-panel `meta.emittedFields` to machine.json (rotatingMachine) and
machineGroup.json (MGC) templates. Each non-row panel declares the Influx
field paths it visualizes, so a parent template's composer can filter out
panels already covered by its children (#39 no-data-duplication rule).

- config/machine.json: 13 non-row panels annotated.
- config/machineGroup.json: panels annotated.
- src/specificClass.js: collectEmittedFields(dashboard) helper.
- test/basic/slice37-emitted-fields.basic.test.js: 4 cases (template loads
  with annotations, aggregation, missing-meta graceful, null input).

PRD F-6 panel set audit: machine.json already covers all the PRD-required
panels (State/Mode/Ctrl%/Runtime/NCog%/Flow/Efficiency/Pressure/Temperature/
Diagnostics) — substantially more than asked. No new panels added.

PRD F-7 predicted-vs-measured side-by-side: deferred. Current architecture
is "1 dashboard per node" (each child gets its own dashboard, cross-linked
from the parent), not "1 dashboard with N composed panels." Side-by-side
rendering of predicted (rotatingMachine dashboard) + measured (measurement
child dashboard) lives naturally as drill-down navigation today. Refactor
to a single-dashboard composition model would be substantial — flagged in
the issue comment for v2 if the drill-down UX proves insufficient.

Closes #37

src/specificClass.js

@@ -105,6 +105,18 @@ class DashboardApi {
     return JSON.parse(raw);
   }
 
+  // Collect every `meta.emittedFields` declared by panels in a template.
+  // Used by #39's parent panel filter — a parent panel whose emittedFields
+  // are fully covered by its children's panels is removed.
+  collectEmittedFields(dashboard) {
+    const out = new Set();
+    for (const panel of dashboard?.panels || []) {
+      const fields = panel?.meta?.emittedFields;
+      if (Array.isArray(fields)) for (const f of fields) out.add(f);
+    }
+    return out;
+  }
+
   grafanaUpsertUrl() {
     const { protocol, host, port } = this.config.grafanaConnector;
     return `${protocol}://${host}:${port}/api/dashboards/db`;