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/tools/delegate-task/model-string-parser.ts

@@ -0,0 +1,63 @@
+const KNOWN_VARIANTS = new Set([
+  "low",
+  "medium",
+  "high",
+  "xhigh",
+  "max",
+  "minimal",
+  "none",
+  "auto",
+  "thinking",
+])
+
+export function parseVariantFromModelID(rawModelID: string): { modelID: string; variant?: string } {
+  const trimmedModelID = rawModelID.trim()
+  if (!trimmedModelID) {
+    return { modelID: "" }
+  }
+
+  const parenthesizedVariant = trimmedModelID.match(/^(.*)\(([^()]+)\)\s*$/)
+  if (parenthesizedVariant) {
+    const modelID = parenthesizedVariant[1]?.trim() ?? ""
+    const variant = parenthesizedVariant[2]?.trim()
+    return variant ? { modelID, variant } : { modelID }
+  }
+
+  const spaceVariant = trimmedModelID.match(/^(.*\S)\s+([a-z][a-z0-9_-]*)$/i)
+  if (spaceVariant) {
+    const modelID = spaceVariant[1]?.trim() ?? ""
+    const variant = spaceVariant[2]?.trim().toLowerCase()
+    if (variant && KNOWN_VARIANTS.has(variant)) {
+      return { modelID, variant }
+    }
+  }
+
+  return { modelID: trimmedModelID }
+}
+
+export function parseModelString(
+  model: string,
+): { providerID: string; modelID: string; variant?: string } | undefined {
+  const trimmedModel = model.trim()
+  if (!trimmedModel) return undefined
+
+  const parts = trimmedModel.split("/")
+  if (parts.length < 2) {
+    return undefined
+  }
+
+  const providerID = parts[0]?.trim()
+  const rawModelID = parts.slice(1).join("/").trim()
+  if (!providerID || !rawModelID) {
+    return undefined
+  }
+
+  const parsedModel = parseVariantFromModelID(rawModelID)
+  if (!parsedModel.modelID) {
+    return undefined
+  }
+
+  return parsedModel.variant
+    ? { providerID, modelID: parsedModel.modelID, variant: parsedModel.variant }
+    : { providerID, modelID: parsedModel.modelID }
+}