feat: add diff-review slash command for local code review

Add custom slash command to review git diffs from an architect's perspective.
The command analyzes code quality, architecture, maintainability, and project
standards to provide actionable feedback on uncommitted changes.

.claude/commands/diff-review.md

@@ -0,0 +1,56 @@
+---
+description: Review current git diff from an architect's perspective
+allowed-tools: Bash(git diff), Bash(git diff --cached), Bash(git status --short), Read, Grep, Glob
+---
+
+Analyze the current git diff (both staged and unstaged changes) from a senior architect's perspective.
+
+## Review Checklist
+
+### 1. Code Quality & Simplicity
+- Is the code unnecessarily complex? Could it be simplified?
+- Are variable/function names clear and self-documenting?
+- Is the logic flow easy to follow?
+- Any code duplication that should be extracted?
+
+### 2. Architecture & Design
+- Do changes align with the project's overall architecture?
+- Are design patterns used appropriately?
+- Is there proper separation of concerns?
+- Are dependencies minimal and well-managed?
+
+### 3. File Organization
+- Check if any files exceed 200 lines and need splitting
+- Are methods/functions kept under 30 lines?
+- Is related functionality properly grouped?
+- Should any code be moved to different modules?
+
+### 4. Standards & Best Practices
+- Would the code pass linting (TypeScript: strict mode, Go: go fmt/vet)?
+- Is formatting consistent with project standards?
+- Are there missing type annotations or error handling?
+- Any obvious security concerns or performance issues?
+
+### 5. Maintainability
+- Is the code easy for a junior developer to understand?
+- Are there any TODOs, FIXMEs, or hacks that need addressing?
+- Would this code be easy to test?
+- Are edge cases handled appropriately?
+
+### 6. Project-Specific Guidelines
+Consider CLAUDE.md guidelines:
+- Clean, simple, short methods
+- Files should not exceed 200 lines
+- Code should be understandable by junior developers
+- Visual aids (ASCII diagrams) for complex concepts where helpful
+
+## Review Process
+1. First, check git status to understand scope of changes
+2. Review unstaged changes (git diff)
+3. Review staged changes (git diff --cached)
+4. For each changed file, evaluate against the checklist
+5. Provide specific, actionable feedback with file:line references
+6. Suggest concrete improvements or refactoring if needed
+7. If files are getting large, recommend specific splits
+
+Arguments: $ARGUMENTS