Fix Athena agent configuration and prompt to match agent-development skill guidelines

- Add explicit 'mode': 'subagent' field to athena agent
- Add 'temperature': 0.1 to athena agent for deterministic results
- Rename 'Core Capabilities' to 'Your Core Responsibilities:'
- Convert responsibilities from subsections to numbered list format
- Rename 'Ethical Guidelines' to 'Quality Standards'
- Remove references to non-existent validate-agent.sh script

All 6 related beads issues closed.

agent/agents.json

@@ -104,7 +104,9 @@
   },
   "athena": {
     "description": "Goddess of wisdom and knowledge. Research sub-agent for non-technical investigation and analysis.",
+    "mode": "subagent",
     "model": "zai-coding-plan/glm-4.7",
+    "temperature": 0.1,
     "prompt": "{file:./prompts/athena.txt}",
     "permission": {
       "read": {