Unify chat.py and conversation.py into single implementation

CRITICAL FIX: chat.py had TWO execution paths causing inconsistent behavior:
1. Tool calling (correct) - used centralized command_patterns
2. Legacy JSON command parsing (broken) - bypassed SysadminTools

This caused macha-chat to fail SSH connections while macha-ask worked.

Changes:
- Rewrote chat.py to use ONLY tool-calling architecture
- All commands now go through SysadminTools.execute_command()
- SSH commands use centralized command_patterns.py
- conversation.py is now a lightweight wrapper for compatibility
- Both macha-chat and macha-ask use the same code path
- Updated module.nix to call chat.py directly

Benefits:
- Consistent behavior between macha-chat and macha-ask
- Single execution path = easier to maintain
- All SSH commands use explicit key paths
- No more password prompts

Fixes:
- SSH from macha-chat now works correctly
- Both interfaces use centralized command patterns

module.nix

@@ -507,7 +507,7 @@ print('='*60)
         "
       '')
       
-      # Tool to ask Macha questions
+      # Tool to ask Macha questions (unified with macha-chat, uses ask_main entry point)
       (pkgs.writeScriptBin "macha-ask" ''
         #!${pkgs.bash}/bin/bash
         if [ $# -eq 0 ]; then
@@ -515,7 +515,8 @@ print('='*60)
           echo "Example: macha-ask Why did you recommend restarting that service?"
           exit 1
         fi
-        sudo -u ${cfg.user} ${pkgs.coreutils}/bin/env CHROMA_ENV_FILE="" ANONYMIZED_TELEMETRY="False" ${pythonEnv}/bin/python3 ${./.}/conversation.py "$@"
+        # Run as macha user with ask_main entry point from chat.py
+        sudo -u ${cfg.user} ${pkgs.coreutils}/bin/env PYTHONPATH=${toString ./.} CHROMA_ENV_FILE="" ANONYMIZED_TELEMETRY="False" ${pythonEnv}/bin/python3 -c "from chat import ask_main; ask_main()" "$@"
       '')
       
       # Issue tracking CLI