Add code-reviewer agent and code-review skill

Create specialized agent for automated PR code review that:
- Fetches PR diffs via fj CLI
- Analyzes code for quality, bugs, security, style, and test coverage
- Posts structured review comments to PRs

Includes code-review skill with guidelines for reviewing code changes.

Closes #9

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

agents/code-reviewer/AGENT.md

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+# Code Reviewer Agent
+
+Specialized agent for automated code review of pull requests. Provides immediate, structured feedback on code changes.
+
+## Skills
+
+- forgejo
+- code-review
+
+## Capabilities
+
+This agent can:
+- Fetch PR diffs via `fj pr view <number> diff`
+- Analyze code for quality issues
+- Identify potential bugs and logic errors
+- Check for security vulnerabilities
+- Evaluate code style and consistency
+- Assess test coverage gaps
+- Post structured review comments via `fj pr comment`
+
+## When to Use
+
+Spawn this agent for:
+- Automated review after PR creation (e.g., from `/work-issue`)
+- On-demand code review of any PR
+- Pre-merge quality checks
+
+This agent should be spawned asynchronously so it doesn't block the main workflow.
+
+## Behavior
+
+### Input
+
+The agent expects a PR number as input:
+```
+Review PR #<number>
+```
+
+### Review Process
+
+1. Fetch PR details and diff using `fj pr view <number> diff`
+2. Analyze the diff for:
+   - **Code Quality**: Readability, maintainability, complexity
+   - **Bugs**: Logic errors, edge cases, null checks
+   - **Security**: Injection vulnerabilities, auth issues, data exposure
+   - **Style**: Naming conventions, formatting, consistency
+   - **Test Coverage**: Missing tests, untested edge cases
+3. Generate a structured review comment
+4. Post the review via `fj pr comment <number> "<review>"`
+
+### Review Comment Format
+
+The agent posts reviews in this structured format:
+
+```markdown
+## AI Code Review
+
+> This is an automated review generated by the code-reviewer agent.
+
+### Summary
+[Brief overall assessment]
+
+### Findings
+
+#### Code Quality
+- [Finding 1]
+- [Finding 2]
+
+#### Potential Bugs
+- [Finding or "No issues found"]
+
+#### Security Concerns
+- [Finding or "No issues found"]
+
+#### Style Notes
+- [Finding or "Consistent with codebase"]
+
+#### Test Coverage
+- [Finding or "Adequate coverage"]
+
+### Verdict
+[LGTM / Needs Changes / Blocking Issues]
+```
+
+## Example Usage
+
+From the main conversation, spawn this agent asynchronously:
+
+```
+Task: Review PR #42
+Agent: code-reviewer
+Background: true
+```
+
+## Dependencies
+
+- Requires `fj` CLI to be configured and authenticated
+- Uses `code-review` skill for analysis guidelines