feat: Media Generation Plugin Suite + GitHub Integration (Issue #20)

[om952]

• media-core — Shared infrastructure package with storage wrapper, job queue, cost tracker, retry logic, and shared types
• media-image — Image generation plugin with Stable Diffusion (self-hosted) and DALL-E (OpenAI API) backends, plus generate_image tool
• media-video — Video generation plugin with ComfyUI (self-hosted SVD), FFmpeg (local slideshows), and Runway (API) backends, plus generate_video tool
• media-audio — Audio/TTS generation plugin with ElevenLabs (API) and Edge TTS (free system) backends, plus generate_audio tool
• media-dashboard — UI plugin with GalleryWidget and GenerationStatus components for browsing generated media
• Workspace integration — All packages wired into pnpm workspace with TypeScript configs, builds passing
• Integration guide — packages/plugins/media-suite-INTEGRATION.md with setup, configuration, and usage instructions
• Implementation plan — doc/plans/2026-06-18-media-generation-plugin-suite.md documenting the 6-phase approach

Also includes: GitHub integration plugin (Issue #15).

Verification

# Build all media packages
pnpm --filter @paperclipai/media-core build
pnpm --filter @paperclipai/media-image build
pnpm --filter @paperclipai/media-video build
pnpm --filter @paperclipai/media-audio build
pnpm --filter @paperclipai/media-dashboard build

# Full workspace typecheck
pnpm -r typecheck

# Run tests
pnpm test

Manual verification steps:

1. Install media-image plugin via API: POST /api/plugins/install with {"pluginId": "paperclip.media-image"}
2. Configure DALL-E API key or Stable Diffusion URL in plugin settings
3. Create agent with tools: ["generate_image"]
4. Assign issue with prompt like "Generate a logo for our company"
5. Verify job appears in queue, asset stored, cost logged

Risks

• Low to medium. All plugins are additive and do not modify core Paperclip logic.
• Self-hosted backends (Stable Diffusion, ComfyUI, FFmpeg, Edge TTS) require external binaries/servers — plugin gracefully degrades if unavailable.
• API-based backends (DALL-E, Runway, ElevenLabs) require valid API keys — misconfigured keys fail with logged errors.
• Plugin state (key-value) used for asset metadata storage — no DB access means search/list operations are limited to what state keys can retrieve.
• Cost estimates are approximate and may not match actual vendor billing.

Closes #20