fix(ci): update staging smoke + synth E2E default model slug MiniMax-M2 → MiniMax-M2.7 (#1997)

The bare MiniMax-M2 slug was invalidated by core#2263 deploy-skew fix.
Staging CP now returns 400 on workspace provision when the model slug
is MiniMax-M2; the valid staging slug is MiniMax-M2.7.

This fixes two scheduled main-red workflows:
- continuous-synth-e2e.yml: default model_slug input
- staging-smoke.yml: hardcoded E2E_MODEL_SLUG env

Both were failing with HTTP 400 at workspace provision step.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/continuous-synth-e2e.yml

@@ -118,7 +118,7 @@ jobs:
     timeout-minutes: 20
     env:
       # claude-code default: cold-start ~5 min (comparable to langgraph),
-      # but uses MiniMax-M2 via the template's third-party-
+      # but uses MiniMax-M2.7 via the template's third-party-
       # Anthropic-compat path (workspace-configs-templates/claude-code-
       # default/config.yaml:64-69). MiniMax is ~5-10x cheaper than
       # gpt-4.1-mini per token AND avoids the recurring OpenAI quota-
@@ -131,9 +131,9 @@ jobs:
       # on the per-runtime default ("sonnet" → routes to direct
       # Anthropic, defeats the cost saving). Operators can override
       # via workflow_dispatch by setting a different E2E_MODEL_SLUG
-      # input if they need to exercise a specific model. MiniMax-M2 is the
-      # stable staging MiniMax path used by the full-SaaS smoke.
-      E2E_MODEL_SLUG: ${{ github.event.inputs.model_slug || 'MiniMax-M2' }}
+      # input if they need to exercise a specific model. MiniMax-M2.7 is the
+      # stable staging MiniMax path used by the full-SaaS smoke (#1997).
+      E2E_MODEL_SLUG: ${{ github.event.inputs.model_slug || 'MiniMax-M2.7' }}
       # Bound to 10 min so a stuck provision fails the run instead of
       # holding up the next cron firing. 15-min default in the script
       # is for the on-PR full lifecycle where we have more headroom.

.gitea/workflows/staging-smoke.yml

@@ -112,9 +112,9 @@ jobs:
       E2E_RUNTIME: claude-code
       # Pin the smoke to a specific MiniMax model rather than relying
       # on the per-runtime default (which could resolve to "sonnet" →
-      # direct Anthropic and defeat the cost saving). MiniMax-M2 is the
-      # stable staging MiniMax path used by the full-SaaS smoke.
-      E2E_MODEL_SLUG: MiniMax-M2
+      # direct Anthropic and defeat the cost saving). MiniMax-M2.7 is the
+      # stable staging MiniMax path used by the full-SaaS smoke (#1997).
+      E2E_MODEL_SLUG: MiniMax-M2.7
       E2E_RUN_ID: "smoke-${{ github.run_id }}"
       # Debug-only: when an operator dispatches with keep_on_failure=true,
       # the smoke script's E2E_KEEP_ORG=1 path skips teardown so the