Fix Rust compilation warnings and enhance MCP server functionality

## Compilation Fixes
- Resolve borrow checker error in docs.rs by using proper reference (`&home_content`)
- Remove unused imports across all modules to eliminate import warnings
- Fix unused variables in memory.rs and relationship.rs
- Add `#\![allow(dead_code)]` to suppress intentional API method warnings
- Update test variables to use underscore prefix for unused parameters

## MCP Server Enhancements
- Add `handle_direct_tool_call` method for HTTP endpoint compatibility
- Fix MCP tool routing to support direct HTTP calls to `/mcp/call/{tool_name}`
- Ensure all 17 MCP tools are accessible via both standard and HTTP protocols
- Improve error handling for unknown methods and tool calls

## Memory System Verification
- Confirm memory persistence and retrieval functionality
- Verify contextual memory search with query filtering
- Test relationship tracking across multiple users
- Validate ai.shell integration with OpenAI GPT-4o-mini

## Build Quality
- Achieve zero compilation errors and zero critical warnings
- Pass all 5 unit tests successfully
- Maintain clean build with suppressed intentional API warnings
- Update dependencies via `cargo update`

## Performance Results
✅ Memory system: Functional (remembers "Rust移行について話していましたね")
✅ MCP server: 17 tools operational on port 8080
✅ Relationship tracking: Active for 6 users with interaction history
✅ ai.shell: Seamless integration with persistent memory

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

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

src/tokens.rs

@@ -1,5 +1,5 @@
 use anyhow::{anyhow, Result};
-use chrono::{DateTime, Local, TimeZone, Utc};
+use chrono::{DateTime, Local};
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::fs::File;