feat: add Pi provider support, fix community health files, recategorize /onboard

- Add first-class Pi (pi.dev) provider with transformer, tests, and build integration
- Fix CODEOWNERS username (@paulbakaus → @pbakaus)
- Add missing providers to issue/PR templates (Copilot, Kiro, OpenCode, Pi)
- Add Pi and OpenCode logos to homepage hero and install sections
- Move /onboard from "system" to "enhancement" category
- Update README and DEVELOP.md with all supported providers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/lib/transformers/index.js

@@ -5,3 +5,4 @@ export { transformCodex } from './codex.js';
 export { transformAgents } from './agents.js';
 export { transformKiro } from './kiro.js';
 export { transformOpenCode } from "./opencode.js";
+export { transformPi } from './pi.js';