feat: add bidirectional comment system and agent input request flow

- Add Comment model and CRUD operations (repository, service layers)
- Add WAITING_FOR_INPUT task state for agent input requests
- Add WebSocket actions for comment.add, comment.get, comment.list
- Add ActionCommentAdded and ActionInputRequested notifications
- Update PromptAgent to return PromptResult with stop reason
- Add e2e test for agent input request flow
- Add PR template for the repository

This enables agents to request input from users by returning
stopReason 'needs_input' which transitions the task to
WAITING_FOR_INPUT state and creates an agent comment.

.github/pull_request_template.md

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+## Description
+
+<!-- Provide a brief description of the changes in this PR -->
+
+## Type of Change
+
+- [ ] Bug fix (non-breaking change which fixes an issue)
+- [ ] New feature (non-breaking change which adds functionality)
+- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
+- [ ] Refactoring (no functional changes)
+- [ ] Documentation update
+- [ ] Tests
+
+## Changes Made
+
+<!-- List the main changes made in this PR -->
+
+- 
+
+## Testing
+
+- [ ] Unit tests pass (`go test ./...`)
+- [ ] Build passes (`go build ./...`)
+- [ ] E2E tests pass (if applicable)
+- [ ] Manual testing performed
+
+## Checklist
+
+- [ ] My code follows the project's coding standards
+- [ ] I have performed a self-review of my code
+- [ ] I have commented my code where necessary
+- [ ] I have updated the documentation (if applicable)
+- [ ] My changes generate no new warnings
+- [ ] Any dependent changes have been merged and published
+
+## Related Issues
+
+<!-- Link any related issues here using #issue_number -->
+
+Closes #
+
+## Screenshots (if applicable)
+
+<!-- Add screenshots to help explain your changes -->
+