fix(metis): switch primary model to claude-sonnet-4-6 + correct AGENTS.md inaccuracies

Source code change:
- src/shared/model-requirements.ts: prepend claude-sonnet-4-6 to metis fallback
  chain so Sonnet becomes the default. Opus 4.7 max remains as the immediate
  fallback for callers who want extra reasoning.
- src/shared/model-requirements.test.ts: update assertion to expect Sonnet
  primary + Opus secondary.

AGENTS.md accuracy fixes (verified against source):
- Agent modes: Sisyphus/Hephaestus are 'primary' (not 'all'); Sisyphus-Junior
  is 'subagent' (not 'all'). Confirmed via 'const MODE: AgentMode = ...' in
  each agent file. Also clarified Prometheus has no agentSources factory and
  is built via buildPrometheusAgentConfig.
- Sisyphus fallback chain: corrected order to kimi-k2.6 → k2p5 → kimi-k2.5
  → gpt-5.5 medium → glm-5 → big-pickle (was missing kimi-k2.5).
- Librarian/Explore: added missing minimax-m2.7 step between -highspeed and
  claude-haiku-4-5.
- Metis chain: removed fictitious gemini-3.1-pro entry.
- Sisyphus-Junior chain: spelled out the actual fallback (was 'user-configurable').
- Temperatures: Sisyphus/Hephaestus do not set explicit temperature (model
  default); Sisyphus-Junior is 0.1 via SISYPHUS_JUNIOR_DEFAULTS.
- Quick category default: gpt-5.4-mini (not gpt-5.4-mini-fast).

Team-mode corrections:
- Eligibility registry has 3 verdicts: eligible (sisyphus, atlas, sisyphus-junior),
  conditional (hephaestus — needs D-36 teammate permission), hard-reject
  (oracle, librarian, explore, multimodal-looker, metis, momus, prometheus).
- Schema has 11 fields, not 4: added max_messages_per_run, max_wall_clock_minutes,
  max_member_turns, base_dir, message_payload_max_bytes, recipient_unread_max_bytes,
  mailbox_poll_interval_ms.
- Hooks: 'team-session-events' is 4 sub-handlers in src/plugin/event.ts
  (team-idle-wake-hint, team-lead-orphan-handler, team-member-error-handler,
  team-member-status-handler), not a single Continuation-tier hook.
- Tier counts now show base + team-mode: ToolGuard 14/15, Transform 5/7.
- Total: 52 base hooks, 59 with team-mode.

Doc cascade for the Metis change:
- docs/guide/orchestration.md, agent-model-matching.md, installation.md
- docs/reference/configuration.md, features.md

src/shared/model-requirements.test.ts

@@ -176,20 +176,24 @@ describe("AGENT_MODEL_REQUIREMENTS", () => {
     expect(primary.variant).toBe("max")
   })
 
-  test("metis has claude-opus-4-7 as primary", () => {
+  test("metis has claude-sonnet-4-6 as primary", () => {
     // #given - metis agent requirement
     const metis = AGENT_MODEL_REQUIREMENTS["metis"]
 
     // #when - accessing Metis requirement
-    // #then - claude-opus-4-7 is first
+    // #then - claude-sonnet-4-6 is first, claude-opus-4-7 max is the immediate fallback
     expect(metis).toBeDefined()
     expect(metis.fallbackChain).toBeArray()
     expect(metis.fallbackChain.length).toBeGreaterThan(1)
 
     const primary = metis.fallbackChain[0]
-    expect(primary.model).toBe("claude-opus-4-7")
+    expect(primary.model).toBe("claude-sonnet-4-6")
     expect(primary.providers).toEqual(["anthropic", "github-copilot", "opencode", "vercel"])
-    expect(primary.variant).toBe("max")
+    expect(primary.variant).toBeUndefined()
+
+    const opusFallback = metis.fallbackChain[1]
+    expect(opusFallback.model).toBe("claude-opus-4-7")
+    expect(opusFallback.variant).toBe("max")
 
     const openAiFallback = metis.fallbackChain.find((entry) => entry.providers.includes("openai"))
     expect(openAiFallback).toEqual({

src/shared/model-requirements.ts

@@ -124,6 +124,10 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
   },
   metis: {
     fallbackChain: [
+      {
+        providers: ["anthropic", "github-copilot", "opencode", "vercel"],
+        model: "claude-sonnet-4-6",
+      },
       {
         providers: ["anthropic", "github-copilot", "opencode", "vercel"],
         model: "claude-opus-4-7",