fix: sync all version files to 0.30.2 and add CI check

The 0.30.2 bump was done manually and missed several files:
- .claude-plugin/plugin.json (was 0.30.0)
- .claude-plugin/marketplace.json (was 0.30.0)
- npm-package/package.json (was 0.30.1)
- integrations/beads-mcp/pyproject.toml (was 0.30.1)
- integrations/beads-mcp/src/beads_mcp/__init__.py (was 0.30.1)

Added scripts/check-versions.sh and CI job to prevent this in future.
Always use scripts/bump-version.sh for version bumps.

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

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

.claude-plugin/marketplace.json

@@ -9,7 +9,7 @@
       "name": "beads",
       "source": "./",
       "description": "AI-supervised issue tracker for coding workflows",
-      "version": "0.30.0"
+      "version": "0.30.2"
     }
   ]
 }

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "beads",
   "description": "AI-supervised issue tracker for coding workflows. Manage tasks, discover work, and maintain context with simple CLI commands.",
-  "version": "0.30.0",
+  "version": "0.30.2",
   "author": {
     "name": "Steve Yegge",
     "url": "https://github.com/steveyegge"