feat(routing): add tiers.yaml + rename spec/review-arch templates to airouter

W1 stage-routing work:
- model-registry/tiers.yaml: defines planning/spec-test/coding tier floors
  (complexity≥9/creativity≥9/context≥9 | spec_adherence≥9/test_pass_rate≥9 |
  spec_adherence≥7/test_pass_rate≥7) with qualifies_today lists
- spec-draft-airouter@2.yaml: honest name for what was spec-draft-opus@1
  (always ran Qwen3.6/airouter, not Opus)
- review-spec-arch-airouter@1.yaml: honest name for review-spec-arch-opus@1

Old @1 files kept for in-flight task backward-compatibility.

Claude-Session: https://claude.ai/code/session_01B35bPAKv5uyW1F9gzMcRN7

model-registry/tiers.yaml

@@ -0,0 +1,56 @@
+# Model capability tiers for typed-pipeline routing.
+#
+# Each tier defines score floors (against model-registry/*.yaml `scores` dimensions).
+# The CP picks the cheapest registry entry meeting ALL floors (MR-9/MR-11 — cheapest-wins).
+#
+# Stages that need a specific tier set `tier:` on their `kind: agent` node (W2).
+# Until W2 lands, templates hardcode `model:` directly and these floors serve as
+# documentation of the intended constraint.
+#
+# See claude/stage-routing.md for the authoritative pipeline stage map.
+
+tiers:
+
+  planning:
+    description: >
+      Judgment-heavy work: plan generation, spec re-draft (replan-spec-opus),
+      architecture review escalation (review-spec-opus). Requires sustained
+      reasoning over large context windows.
+    min_scores:
+      complexity: 9
+      creativity: 9
+      context_utilisation: 9
+    qualifies_today:
+      - deepseek-v4flash       # benchmark-inflated 9s; hold to allowed_models ceiling
+      - minimax
+      - claude-opus-4
+    note: >
+      WF-SCH-14 allowed_models ceiling remains authoritative until M7 observed-score
+      recalibration corrects benchmark-inflated registry entries.
+
+  spec-test:
+    description: >
+      Spec-adherent structured work: spec drafting, spec arch review, scope/decompose,
+      test writing, impl review, merge verdict. Needs reliable spec adherence and
+      test execution.
+    min_scores:
+      spec_adherence: 9
+      test_pass_rate: 9
+    qualifies_today:
+      - minimax
+      - claude-sonnet-4
+      - claude-opus-4
+
+  coding:
+    description: >
+      Narrow TDD implementation against pre-validated tests. Lower floors because
+      tests already constrain the solution space.
+    min_scores:
+      spec_adherence: 7
+      test_pass_rate: 7
+    qualifies_today:
+      - airouter-qwen3
+      - airouter-deepseekv4flash
+      - minimax
+      - claude-sonnet-4
+      - claude-opus-4