feat: Bundle core plugins into claude-code repo

Add bundled plugins from claude-code-marketplace into a new plugins/ directory:
- agent-sdk-dev: Development kit for Claude Agent SDK with TypeScript/Python verifiers
- ireview-plugin: Comprehensive AI+Human PR review toolkit with 9 specialized agents
- commit-commands: Git commit workflow commands (commit, push, PR creation)

Created .claude-plugin/marketplace.json at repo root to register the bundled plugins.

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

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

plugins/commit-commands/commands/commit.md

@@ -0,0 +1,17 @@
+---
+allowed-tools: Bash(git add:*), Bash(git status:*), Bash(git commit:*)
+description: Create a git commit
+---
+
+## Context
+
+- Current git status: !`git status`
+- Current git diff (staged and unstaged changes): !`git diff HEAD`
+- Current branch: !`git branch --show-current`
+- Recent commits: !`git log --oneline -10`
+
+## Your task
+
+Based on the above changes, create a single git commit.
+
+You have the capability to call multiple tools in a single response. Stage and create the commit using a single message. Do not use any other tools or do anything else. Do not send any other text or messages besides these tool calls.