fix(aliases): stop rewriting canonical claude-opus-4-6-thinking

The claude-thinking-legacy-alias pattern previously matched both
claude-opus-4-6-thinking and claude-opus-4-7-thinking and mapped
them to claude-opus-4-7. After models.dev started shipping
claude-opus-4-6-thinking as a real canonical model (e.g.
302ai/claude-opus-4-6-thinking), the pattern collides with the
snapshot and trips the pattern-alias-collides-with-snapshot
guardrail in collectModelCapabilityGuardrailIssues, which is what
has been failing the refresh-model-capabilities cron since
2026-04-20.

Tightening the regex to only match claude-opus-4-7-thinking
preserves the legacy-id rewrite for the still-non-canonical
4-7-thinking form while letting 4-6-thinking resolve to itself.

Refs #3635

src/shared/model-capability-aliases.test.ts

@@ -107,4 +107,14 @@ describe("model-capability-aliases", () => {
       ruleID: "claude-thinking-legacy-alias",
     })
   })
+
+  test("treats claude-opus-4-6-thinking as canonical, not as a legacy alias", () => {
+    const result = resolveModelIDAlias("claude-opus-4-6-thinking")
+
+    expect(result).toEqual({
+      requestedModelID: "claude-opus-4-6-thinking",
+      canonicalModelID: "claude-opus-4-6-thinking",
+      source: "canonical",
+    })
+  })
 })