feat: dashboard PR preview bot #541

[Sulamoney222]

Overview

This PR adds a dashboard preview PR-comment bot that renders panel preview PNGs and JSON diffs into PR comments so reviewers can inspect Grafana dashboard changes visually — without leaking internal dashboards to public forks.

Related Issue

Closes #541

Changes

Dashboard preview bot

• [ADD] scripts/dashboard-preview-bot.ts

  • Diffs ops/dashboards/*.json by panel id (added / removed / modified).
  • Renders schematic panel preview PNGs with a minimal zlib-based encoder (no new deps).
  • Posts JSON diff (truncated for large dashboards) + panel change summary.
  • Suppresses content on fork PRs (HEAD_REPO missing treated as unsafe on pull_request).

• [ADD] .github/workflows/dashboard-preview.yml

  • Path-filtered on dashboard JSON; skips forks at the job if level; uploads PNG artifacts.

• [ADD] scripts/__tests__/dashboard-preview-bot.test.ts

  • Edge cases: deleted dashboard/panel, invalid JSON, large diffs, fork suppression, PNG generation.

• [ADD] docs/dashboard-preview-bot.md

Verification Results

npm test -- --testPathPattern=dashboard-preview-bot --coverage=false
✅ 27/27 passed

Acceptance Criteria	Status
Render panels to PNG	✅ Minimal PNG encoder + panel cards
Post images + JSON diff in comment	✅ Data-URI embed / artifact note + truncated diff
Suppress on forks (no leak)	✅ Workflow if + script isForkPr()
Edge: large / deleted panel / non-JSON	✅ Covered in unit tests

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