chore: add knip for unused export/dependency detection

Adds `pnpm check:unused` script powered by knip. Initial run finds
17 unused files, 3 unused deps, 96 unused exports, and 117 unused
exported types — all candidates for cleanup.

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

knip.json

@@ -0,0 +1,30 @@
+{
+  "$schema": "https://unpkg.com/knip@latest/schema.json",
+  "ignore": [".claude/**", "backups/**", "samples/**"],
+  "ignoreDependencies": ["@capakraken/eslint-config", "@capakraken/tsconfig", "turbo"],
+  "ignoreBinaries": ["playwright"],
+  "workspaces": {
+    "apps/web": {
+      "ignore": ["src/**/*.test.{ts,tsx}", "e2e/**"]
+    },
+    "packages/shared": {},
+    "packages/db": {
+      "entry": [
+        "src/index.ts",
+        "src/seed*.ts",
+        "src/reset-*.ts",
+        "src/generate-*.ts",
+        "src/update-*.ts",
+        "src/*.mjs"
+      ],
+      "ignoreDependencies": ["exceljs"]
+    },
+    "packages/engine": {},
+    "packages/staffing": {},
+    "packages/application": {},
+    "packages/api": {},
+    "tooling/eslint": {
+      "entry": ["src/*.js"]
+    }
+  }
+}