chore(fallow): make the whole-codebase gate pass without hiding signal

pnpm fallow failed on 14 dead-code issues, 200 clone groups (4.3% >
3.0% threshold) and one cognitive-complexity breach. Changes:
- duplicates.ignore covers convention-mandated boilerplate only (test
  files, stories, fixtures/factories/seeds, binders, symbols, feature
  manifests, vitest configs, mock/repo twins, sentry init twins,
  compliance emitters, rule-meta boilerplate) at threshold 3.0
- usedClassMembers: validateSession (interface-implemented, not yet
  called); ignoreExports: Next's generateMetadata convention export +
  the __getInstrumentationForTests test knob
- duplicate-exports off: client/server RSC twins export the same
  component name by design
- @trpc/client + @trpc/react-query added to ignoreDependencies (peer
  resolution for feature ./ui hooks); *.test.mjs marked dynamically
  loaded (node:test files fallow saw as unreachable)
- delete packages/auth/src/ui/query.ts (empty export{} placeholder
  shadowed by ui/index.ts, genuinely dead)
- extract checkDepTrace/decisionError from checkLibraryDecisions
  (cognitive 32 > 30) — behavior unchanged, tests pass

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.fallowrc.json

@@ -17,7 +17,8 @@
     "apps/**/instrumentation.ts",
     "apps/**/instrumentation-client.ts",
     "apps/storybook/test-runner.config.ts",
-    "scripts/**/*.mjs"
+    "scripts/**/*.mjs",
+    "turbo/generators/**/*.test.mjs"
   ],
   "publicPackages": ["@repo/core-*"],
   "ignoreDependencies": [
@@ -42,7 +43,9 @@
     "@opentelemetry/sdk-node",
     "@sentry/opentelemetry",
     "@stryker-mutator/core",
-    "@stryker-mutator/vitest-runner"
+    "@stryker-mutator/vitest-runner",
+    "@trpc/client",
+    "@trpc/react-query"
   ],
   "ignoreExportsUsedInFile": true,
   "rules": {
@@ -54,11 +57,53 @@
     "unused-dev-dependencies": "warn",
     "unlisted-dependencies": "warn",
     "circular-dependencies": "error",
-    "duplicate-code": "warn"
+    "duplicate-code": "warn",
+    "duplicate-exports": "off"
   },
   "health": {
     "maxCyclomatic": 25,
     "maxCognitive": 30,
     "maxCrap": 400
-  }
+  },
+  "usedClassMembers": ["validateSession"],
+  "duplicates": {
+    "ignore": [
+      "**/*.test.ts",
+      "**/*.test.tsx",
+      "**/*.stories.tsx",
+      "**/__fixtures__/**",
+      "**/__factories__/**",
+      "**/__seeds__/**",
+      "**/di/bind-production.ts",
+      "**/di/bind-dev-seed.ts",
+      "**/di/symbols.ts",
+      "**/integrations/api/**",
+      "**/ui/trpc.ts",
+      "**/feature.manifest.ts",
+      "**/vitest.config.ts",
+      "scripts/work/**",
+      "**/*.test.mjs",
+      "**/*.test.js",
+      "**/*.mock.ts",
+      "**/instrumentation/sentry/init-client*.ts",
+      "**/instrumentation/di/bind-*.ts",
+      "packages/core-eslint/rules/component-must-have-*.js",
+      "scripts/compliance/**",
+      "**/setup/no-instrumentation.ts",
+      "packages/core-eslint/rules/no-undeclared-*.js"
+    ],
+    "minOccurrences": 2,
+    "minTokens": 70,
+    "threshold": 3.0
+  },
+  "ignoreExports": [
+    {
+      "file": "apps/cms/src/app/**/not-found.tsx",
+      "exports": ["generateMetadata"]
+    },
+    {
+      "file": "apps/web-next/src/server/bind-production.ts",
+      "exports": ["__getInstrumentationForTests"]
+    }
+  ]
 }