docs: Update all documentation to reflect v5.4.0 skill-based search

Documentation Updates:
- README.md: Updated version badge, What's New, and search section
- docs/usage/search-tools.mdx: Rewrote for skill-based natural language approach
- docs/architecture/mcp-search.mdx → search-architecture.mdx: Complete rewrite
- docs/architecture/overview.mdx: Updated components and search pipeline
- docs/usage/getting-started.mdx: Added skill-based search section
- docs/configuration.mdx: Updated search configuration for v5.4.0
- docs/introduction.mdx: Updated key features
- docs/docs.json: Updated navigation to search-architecture

Key Changes:
- Emphasized ~2,250 token savings per session start
- Converted all examples to natural language queries
- Documented 10 HTTP API endpoints
- Explained progressive disclosure pattern
- Added migration notes (transparent, no user action required)
- Removed outdated MCP references

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

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

docs/configuration.mdx

@@ -137,22 +137,19 @@ Hooks are configured in `plugin/hooks/hooks.json`:
 }
 ```
 
-### MCP Server Configuration
+### Search Configuration (v5.4.0+)
 
-The MCP search server is configured in `plugin/.mcp.json`:
+**Migration Note**: As of v5.4.0, Claude-Mem uses skill-based search instead of MCP tools.
 
-```json
-{
-  "mcpServers": {
-    "claude-mem-search": {
-      "type": "stdio",
-      "command": "${CLAUDE_PLUGIN_ROOT}/scripts/search-server.mjs"
-    }
-  }
-}
-```
+**Previous (v5.3.x and earlier)**: MCP search server with 9 tools (~2,500 tokens per session)
+**Current (v5.4.0+)**: Search skill with HTTP API (~250 tokens per session)
 
-This registers the `claude-mem-search` server with Claude Code, making the 9 search tools available in all sessions.
+**No configuration required** - the search skill is automatically available in Claude Code sessions.
+
+Search operations are now provided via:
+- **Skill**: `plugin/skills/search/SKILL.md` (auto-invoked when users ask about past work)
+- **HTTP API**: 10 endpoints on worker service port 37777
+- **Progressive Disclosure**: Full instructions loaded on-demand only when needed
 
 ## PM2 Configuration