feat(phase10): complete MCP-only architecture migration

This commit completes Phase 10 of the MCP migration by removing all
direct provider usage from CLI/TUI and enforcing MCP-first architecture.

## Changes

### Core Architecture
- **main.rs**: Replaced OllamaProvider with RemoteMcpClient
  - Uses MCP server configuration from config.toml if available
  - Falls back to auto-discovery of MCP LLM server binary
- **agent_main.rs**: Unified provider and MCP client to single RemoteMcpClient
  - Simplifies initialization with Arc::clone pattern
  - All LLM communication now goes through MCP protocol

### Dependencies
- **Cargo.toml**: Removed owlen-ollama dependency from owlen-cli
  - CLI no longer knows about Ollama implementation details
  - Clean separation: only MCP servers use provider crates internally

### Tests
- **agent_tests.rs**: Updated all tests to use RemoteMcpClient
  - Replaced OllamaProvider::new() with RemoteMcpClient::new()
  - Updated test documentation to reflect MCP requirements
  - All tests compile and run successfully

### Examples
- **Removed**: custom_provider.rs, basic_chat.rs (deprecated)
- **Added**: mcp_chat.rs - demonstrates recommended MCP-based usage
  - Shows how to use RemoteMcpClient for LLM interactions
  - Includes model listing and chat request examples

### Cleanup
- Removed outdated TODO about MCP integration (now complete)
- Updated comments to reflect current MCP architecture

## Architecture

```
CLI/TUI → RemoteMcpClient (impl Provider)
          ↓ MCP Protocol (STDIO/HTTP/WS)
          MCP LLM Server → OllamaProvider → Ollama
```

## Benefits
- ✅ Clean separation of concerns
- ✅ CLI is protocol-agnostic (only knows MCP)
- ✅ Easier to add new LLM backends (just implement MCP server)
- ✅ All tests passing
- ✅ Full workspace builds successfully

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

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

crates/owlen-tui/src/chat_app.rs

@@ -311,7 +311,7 @@ impl ChatApp {
     pub async fn set_mode(&mut self, mode: owlen_core::mode::Mode) {
         self.operating_mode = mode;
         self.status = format!("Switched to {} mode", mode);
-        // TODO: Update MCP client mode when MCP integration is fully implemented
+        // Mode switching is handled by the SessionController's tool filtering
     }
 
     pub(crate) fn model_selector_items(&self) -> &[ModelSelectorItem] {