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/utils.js

@@ -298,6 +298,11 @@ export const PROVIDER_PLACEHOLDERS = {
     model: 'Claude',
     config_file: 'OPENCODE.md',
     ask_instruction: 'STOP and call the AskUserQuestionTool to clarify.',
+  },
+  'pi': {
+    model: 'the model',
+    config_file: 'AGENTS.md',
+    ask_instruction: 'ask the user directly to clarify what you cannot infer.'
   }
 };