refactor!: major directory restructuring and npx support

- Create agents/ directory, move bmad, requirements, development-essentials
- Remove docs/, hooks/, dev-workflow/ directories
- Add npx support via github:cexll/myclaude
- Add bin/cli.js with --update command for installed modules
- Add package.json, skills/README.md, PLUGIN_README.md
- Update all references across config.json, README, marketplace.json
- Change default module from dev to do
- Update CHANGELOG with all 59 tags

BREAKING CHANGE: Directory structure changed, docs/hooks removed

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Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

agents/development-essentials/.claude-plugin/plugin.json

@@ -0,0 +1,9 @@
+{
+  "name": "essentials",
+  "description": "Essential development commands for coding, debugging, testing, optimization, and documentation",
+  "version": "5.6.1",
+  "author": {
+    "name": "cexll",
+    "email": "cexll@cexll.com"
+  }
+}