fix(coverage): exempt .d.ts files from diff coverage gate

Ambient declaration files have no runtime code so v8 coverage
never generates DA records for them. Without an allowlist entry,
coverage:diff reports no-coverage-data for every .d.ts in the
diff. Add /\.d\.ts$/ to ALLOWED_GLOBS with a companion test.

Also configure @vitest/coverage-v8 for core-shared and add
targeted vitest exclusions for infrastructure files that are not
unit-testable (DI symbols, interface files, tRPC context, Sentry
SDK init) — bringing core-shared into the L2 aggregate and making
the L1 diff gate enforce coverage on new executable code.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

coverage/summary.json

@@ -1,18 +1,18 @@
 {
-  "generatedAt": "2026-05-18T18:22:54.558Z",
-  "commit": "c298f39",
+  "generatedAt": "2026-05-18T18:25:58.074Z",
+  "commit": "a94e803",
   "repo": {
     "statements": 96.34,
-    "branches": 91.4,
-    "functions": 96.75,
+    "branches": 91.41,
+    "functions": 96.76,
     "lines": 96.34,
     "counts": {
       "lf": 4100,
       "lh": 3950,
-      "brf": 767,
-      "brh": 701,
-      "fnf": 246,
-      "fnh": 238
+      "brf": 768,
+      "brh": 702,
+      "fnf": 247,
+      "fnh": 239
     }
   },
   "byPackage": {
@@ -60,16 +60,16 @@
     },
     "@repo/core-shared": {
       "statements": 97.75,
-      "branches": 95.52,
-      "functions": 91.49,
+      "branches": 95.54,
+      "functions": 91.58,
       "lines": 97.75,
       "counts": {
         "lf": 935,
         "lh": 914,
-        "brf": 268,
-        "brh": 256,
-        "fnf": 94,
-        "fnh": 86
+        "brf": 269,
+        "brh": 257,
+        "fnf": 95,
+        "fnh": 87
       }
     },
     "@repo/marketing-pages": {