feat(athena): redesign Step 1 routing with two-phase classification and cross-check option

Replace the 3-route system (self-answerable/ambiguous/council-clear) with
6-category first-interaction routing (meta, wrong-agent, council-worthy,
simple/factual, tool/action, ambiguous) plus 2 pre-checks for explicit
opt-out and council requests. Add subsequent-interaction rules for direct
answers, auto-routing, and greetings. Add 'Cross-check with council'
action to all 8 guidance files for post-synthesis re-evaluation.

src/agents/athena/guidance/plan.ts

@@ -20,6 +20,7 @@ Question({
       { label: "Plan selected phase (Prometheus)", description: "Choose one phase for Prometheus to plan. Run /start-work to execute." },
       { label: "Write to document", description: "Save to .sisyphus/athena/notes/ (named after this council session)" },
       { label: "Ask follow-up", description: "Ask another planning question" },
+      { label: "Cross-check with council", description: "Launch a new council session with this synthesis as context" },
       { label: "Done", description: "No further action needed" }
     ],
     multiple: false
@@ -44,5 +45,6 @@ Question({
 - Plan selected phase (Prometheus) -> switch_agent(agent="prometheus") with only the selected phase plus dependencies, framed as work to be planned.
 - Write to document -> write the document to the ".sisyphus/athena/notes/" directory using the council session name from the council_finalize archive_dir, then report the exact path to the user.
 - Ask follow-up -> ask user then restart the council workflow from Step 3 (intent classification).
+- Cross-check with council -> launch a new council session with the current synthesis as context. Restart from Step 2 (council setup) with the synthesis included in the prompt.
 - Done -> acknowledge and end.
 </runtime_action_paths>`