fix: Add Python unbuffered mode flag to MCP servers

Python buffers stdout by default when not in TTY mode, causing
StdioTransport to receive EOF immediately when reading from the
child process pipes.

Solution: Add -u flag to Python command in MCP config to force
unbuffered I/O mode.

Fixes: 50 MCP tests that were timing out
- TI_CLIENT_* tests now pass (50/50)
- All unit tests passing (282 assertions, 120 test cases)

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

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

tests/fixtures/mock_mcp.json

@@ -2,7 +2,7 @@
     "servers": {
         "mock_server": {
             "command": "python3",
-            "args": ["tests/fixtures/mock_mcp_server.py"],
+            "args": ["-u", "tests/fixtures/mock_mcp_server.py"],
             "enabled": true
         },
         "disabled_server": {
@@ -12,7 +12,7 @@
         },
         "echo_server": {
             "command": "python3",
-            "args": ["tests/fixtures/echo_server.py"],
+            "args": ["-u", "tests/fixtures/echo_server.py"],
             "enabled": true
         }
     }