feat(athena): complete delegation routing fix with mode-aware delegation table

- Re-add ATHENA_PROMPT_METADATA with tight triggers and avoidWhen guardrails
- Update switch_agent tool description with permanent handoff guardrail
- Make buildDelegationTable mode-aware: switch_agent for primary, task() for subagent
- Pass agent mode through general-agents to AvailableAgent interface
- Improve primary agent error messages in subagent-resolver with alternatives
- Add council-first bias to Athena interactive prompt
- Update athena-junior trigger text for clearer task() invocation guidance
- Add tests for ATHENA_PROMPT_METADATA shape, triggers, useWhen, avoidWhen

src/tools/switch-agent/tools.ts

@@ -6,7 +6,9 @@ import type { SwitchAgentArgs } from "./types"
 const DESCRIPTION =
   "Switch the active session agent. After calling this tool, the session will transition to the specified agent " +
   "with the provided context as its starting prompt. Use this to route work to another agent " +
-  "(e.g., Atlas for fixes, Prometheus for planning). The switch executes when the current agent's turn completes."
+  "(e.g., Atlas for fixes, Prometheus for planning). The switch executes when the current agent's turn completes.\n\n" +
+  "Permanent one-way handoff. Use ONLY when you're the wrong agent for the overall job, NEVER for subtasks (use task()). " +
+  "Targets: atlas, prometheus, sisyphus, hephaestus, athena (multi-model council)."
 
 const ALLOWED_AGENTS = new Set(["atlas", "prometheus", "sisyphus", "hephaestus", "athena"])