minimax: move to MiniMax-M3.1-Flash-Preview; drop bare minimax/minimax-m2 slugs

- new context minimax-m31-flash/v1 (model pin; no thinking-budget init, Flash
  ignores it); four composites switch from minimax-m3-max/v1 (kept for rollback)
- models + registry for minimax-m31-flash-{max,medium}; removes the dangling
  model-registry/minimax.yaml (endpoint "minimax" never existed)
- tiers, harness-roles, minimax-* task templates and the *-review-loop@1
  workflows use the Flash slugs (MiniMax silently maps unknown names to M3, so
  the provider-id translation lands in agent-runtimes)

model-registry/harness-roles.yaml

@@ -5,5 +5,6 @@ roles:
     claude-sonnet-5: code-sonnet-tdd-repo
     claude-opus-5: code-opus-tdd-repo
     claude-haiku-4-5: code-haiku-tdd-repo
-    minimax: code-minimax-tdd-repo
+    minimax-m31-flash-max: code-minimax-tdd-repo
+    minimax-m31-flash-medium: code-minimax-tdd-repo
     claude-fable-5: code-fable-tdd-repo

model-registry/minimax-m31-flash-max.yaml

@@ -0,0 +1,21 @@
+# agent-runtime-framework — model-registry/ (CRS tag: model-registry)
+# Max-effort Flash; replaces minimax-m3-max in planning/draft-heavy and explicit-model nodes.
+# PLACEHOLDER scores/costs: scores are copied from the M3 entry this replaces and
+# costs are set just below it so cheapest-wins (tiers.yaml) selects Flash over
+# the retained M3 entries. Revisit with observed scores and published pricing.
+name: minimax-m31-flash-max
+endpoint: minimax-m31-flash-max
+provider: minimax
+family: minimax
+scores:
+  complexity: 10
+  test_pass_rate: 9
+  creativity: 10
+  spec_adherence: 9
+  cost_efficiency: 5
+  context_utilisation: 10
+cost_per_1k_tokens:
+  input: 0.0025
+  output: 0.0125
+source: benchmark
+harness_version: null

model-registry/minimax-m31-flash-medium.yaml

@@ -0,0 +1,21 @@
+# agent-runtime-framework — model-registry/ (CRS tag: model-registry)
+# Medium-effort Flash; replaces minimax-m3 in the build/integrate/spec-test/coding tiers.
+# PLACEHOLDER scores/costs: scores are copied from the M3 entry this replaces and
+# costs are set just below it so cheapest-wins (tiers.yaml) selects Flash over
+# the retained M3 entries. Revisit with observed scores and published pricing.
+name: minimax-m31-flash-medium
+endpoint: minimax-m31-flash-medium
+provider: minimax
+family: minimax
+scores:
+  complexity: 8
+  test_pass_rate: 9
+  creativity: 8
+  spec_adherence: 9
+  cost_efficiency: 6
+  context_utilisation: 9
+cost_per_1k_tokens:
+  input: 0.00125
+  output: 0.00625
+source: benchmark
+harness_version: null

model-registry/minimax.yaml

@@ -1,15 +0,0 @@
-name: minimax
-endpoint: minimax
-provider: minimax
-scores:
-  complexity: 10
-  test_pass_rate: 9
-  creativity: 10
-  spec_adherence: 9
-  cost_efficiency: 3
-  context_utilisation: 10
-cost_per_1k_tokens:
-  input: 0.0
-  output: 0.0
-source: benchmark
-harness_version: null

model-registry/tiers.yaml

@@ -22,7 +22,7 @@ tiers:
       context_utilisation: 9
     qualifies_today:
       - deepseek-v4flash       # benchmark-inflated 9s; hold to allowed_models ceiling
-      - minimax
+      - minimax-m31-flash-max
       - claude-opus-5
     note: >
       WF-SCH-14 allowed_models ceiling remains authoritative until M7 observed-score
@@ -37,7 +37,8 @@ tiers:
       spec_adherence: 9
       test_pass_rate: 9
     qualifies_today:
-      - minimax
+      - minimax-m31-flash-max
+      - minimax-m31-flash-medium
       - claude-sonnet-5
       - claude-opus-5
 
@@ -51,7 +52,8 @@ tiers:
     qualifies_today:
       - airouter-qwen3
       - airouter-deepseekv4flash
-      - minimax
+      - minimax-m31-flash-max
+      - minimax-m31-flash-medium
       - claude-sonnet-5
       - claude-opus-5
       - claude-fable-5