feat(athena): split into athena (interactive) and athena-junior (subagent)

Split the Athena council orchestrator into two distinct agents:
- athena: primary mode, interactive prompt with Question tool and switch_agent
- athena-junior: subagent mode, non-interactive prompt with structured JSON output

Key changes:
- Create athena-junior-agent.ts factory (mode=subagent, denies question+call_omo_agent)
- Revert athena agent.ts to primary mode (no env var switching)
- Make buildAthenaRuntimeGuidance mode-aware (strips action_paths for non-interactive)
- Add mode parameter to council_finalize tool
- Register athena-junior in builtin-agents, tool-config, model-requirements
- Replace "athena" with "athena-junior" in call_omo_agent ALLOWED_AGENTS
- Update all tests for new architecture

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/model-requirements.ts

@@ -190,6 +190,16 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
       { providers: ["google", "github-copilot", "opencode"], model: "gemini-3-pro", variant: "high" },
     ],
   },
+  "athena-junior": {
+    fallbackChain: [
+      { providers: ["anthropic", "github-copilot", "opencode"], model: "claude-opus-4-6", variant: "max" },
+      { providers: ["opencode"], model: "kimi-k2.5-free" },
+      { providers: ["zai-coding-plan"], model: "glm-4.7" },
+      { providers: ["opencode"], model: "glm-4.7-free" },
+      { providers: ["openai", "github-copilot", "opencode"], model: "gpt-5.2", variant: "high" },
+      { providers: ["google", "github-copilot", "opencode"], model: "gemini-3-pro", variant: "high" },
+    ],
+  },
   "council-member": {
     fallbackChain: [
       { providers: ["opencode"], model: "gpt-5-nano" },