refactor(aliases): migrate to pattern-based model alias resolution

Move from hardcoded exact aliases to pattern-based canonicalization:

- Populate PATTERN_ALIAS_RULES with regex patterns for:
  - Claude thinking variants (claude-opus-4-6-thinking → claude-opus-4-6)
  - Gemini tier suffixes (gemini-3.1-pro-{high,low} → gemini-3.1-pro)
- Add stripProviderPrefixForAliasLookup() for provider-prefixed models
  (anthropic/claude-sonnet-4-6 → claude-sonnet-4-6 for capability lookup)
- Preserve requestedModelID (with prefix) for API transport
- Reduce EXACT_ALIAS_RULES to exceptional cases only
  (gemini-3-pro-{high,low} → gemini-3-pro-preview)
- Comprehensive test coverage for patterns, prefix stripping, negatives

Addresses Discussion #2835 (pattern matching architecture)
Related to PR #2834 (alias guardrails)

41 targeted tests pass, 4467 full suite tests pass, tsc clean.

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

@@ -29,7 +29,7 @@ describe("model-capability-guardrails", () => {
     const brokenSnapshot: ModelCapabilitiesSnapshot = {
       ...bundledSnapshot,
       models: Object.fromEntries(
-        Object.entries(bundledSnapshot.models).filter(([modelID]) => modelID !== "gemini-3.1-pro"),
+        Object.entries(bundledSnapshot.models).filter(([modelID]) => modelID !== "gemini-3-pro-preview"),
       ),
     }
 
@@ -41,13 +41,13 @@ describe("model-capability-guardrails", () => {
     expect(issues).toContainEqual(
       expect.objectContaining({
         kind: "alias-target-missing-from-snapshot",
-        aliasModelID: "gemini-3.1-pro-high",
-        canonicalModelID: "gemini-3.1-pro",
+        aliasModelID: "gemini-3-pro-high",
+        canonicalModelID: "gemini-3-pro-preview",
       }),
     )
   })
 
-  test("flags exact aliases when models.dev gains a canonical entry for the alias itself", () => {
+  test("flags pattern aliases when models.dev gains a canonical entry for the alias itself", () => {
     const bundledSnapshot = getBundledModelCapabilitiesSnapshot()
     const aliasCollisionSnapshot: ModelCapabilitiesSnapshot = {
       ...bundledSnapshot,
@@ -68,13 +68,41 @@ describe("model-capability-guardrails", () => {
 
     expect(issues).toContainEqual(
       expect.objectContaining({
-        kind: "exact-alias-collides-with-snapshot",
-        aliasModelID: "gemini-3.1-pro-high",
+        kind: "pattern-alias-collides-with-snapshot",
+        modelID: "gemini-3.1-pro-high",
         canonicalModelID: "gemini-3.1-pro",
       }),
     )
   })
 
+  test("flags exact aliases when models.dev gains a canonical entry for the alias itself", () => {
+    const bundledSnapshot = getBundledModelCapabilitiesSnapshot()
+    const aliasCollisionSnapshot: ModelCapabilitiesSnapshot = {
+      ...bundledSnapshot,
+      models: {
+        ...bundledSnapshot.models,
+        "gemini-3-pro-high": {
+          id: "gemini-3-pro-high",
+          family: "gemini",
+          reasoning: true,
+        },
+      },
+    }
+
+    const issues = collectModelCapabilityGuardrailIssues({
+      snapshot: aliasCollisionSnapshot,
+      requirementModelIDs: [],
+    })
+
+    expect(issues).toContainEqual(
+      expect.objectContaining({
+        kind: "exact-alias-collides-with-snapshot",
+        aliasModelID: "gemini-3-pro-high",
+        canonicalModelID: "gemini-3-pro-preview",
+      }),
+    )
+  })
+
   test("flags built-in requirement models that rely on aliases instead of canonical IDs", () => {
     const issues = collectModelCapabilityGuardrailIssues({
       requirementModelIDs: ["gemini-3.1-pro-high"],