feat: release v4.0.0 - standalone CLI with multi-LLM support

Major changes:
- Add Claude Max LLM provider (no API key required)
- Add DeepSeek LLM provider
- Add independent ReAct engine module
- Add intent classifier for simple mode
- Restructure documentation into modular guides
- Update version to 4.0.0

New files:
- src/plan_cascade/llm/providers/claude_max.py
- src/plan_cascade/llm/providers/deepseek.py
- src/plan_cascade/core/react_engine.py
- src/plan_cascade/core/intent_classifier.py
- docs/CLI-Guide.md
- docs/Plugin-Guide.md
- docs/Desktop-Guide.md
- docs/System-Architecture.md

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

Author: Taoidle

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "plan-cascade",
-  "version": "3.3.0",
+  "version": "4.0.0",
   "description": "Three-layer cascaded parallel development framework with multi-agent collaboration. Breaks down projects into Features (Mega Plan), Features into Stories (Hybrid Ralph), with dependency-driven batch execution, Git Worktree isolation, and support for multiple AI agents (Codex, Amp, Aider, etc.).",
   "author": {
     "name": "Taoidle",