Complete TODO items in MCP server implementation

**Problem:**
Multiple TODO comments in MCP server files indicate incomplete implementations:

- `src/mcp/server.ts:250` - Tool-specific metrics implementation
- `src/mcp/server.ts:251` - Error categorization implementation
- `src/mcp/session-manager.ts:348` - OAuth authentication
- `src/mcp/claude-code-wrapper.ts:244` - SPARC mode execution
- `src/mcp/auth.ts:283` - OAuth authentication

**Impact:**
Incomplete features may cause runtime errors or limit functionality.

**Solution:**
Review and implement each TODO item or remove if no longer needed.

**Related PR:** https://github.com/KHAEntertainment/claude-flow/pull/2
**Requested by:** @KHAEntertainment

Start by reviewing the TODOs at the specified lines in src/mcp/server.ts, src/mcp/session-manager.ts, src/mcp/claude-code-wrapper.ts, and src/mcp/auth.ts, then compare the related pull request. Done means each TODO has a working implementation or is removed because it is no longer needed; the payload does not name a test command or test file.

Written by the indexing model from the issue text.