refactor: upgrade Biome lint rules

Promote noExplicitAny from warn to error and enable noNonNullAssertion
at warn level. Fix the two resulting errors in src/schema.ts by introducing
a JsonSchema interface to replace the any-typed local variables.

https://claude.ai/code/session_016QvEfqw6YZ3RjwBHrJ4w8S

biome.json

@@ -8,12 +8,12 @@
     "rules": {
       "recommended": true,
       "suspicious": {
-        "noExplicitAny": "warn",
+        "noExplicitAny": "error",
         "noRedundantUseStrict": "off",
         "noImplicitAnyLet": "off"
       },
       "style": {
-        "noNonNullAssertion": "off",
+        "noNonNullAssertion": "warn",
         "useConst": "warn",
         "useNodejsImportProtocol": "off",
         "useTemplate": "off"

src/schema.ts

@@ -105,8 +105,16 @@ export function normalizeCardsPayload(parsed: { cards?: unknown[] }): RawCard[]
     }));
 }
 
-export function cardOutputSchema(strict: boolean) {
-  const cardSchema: any = {
+interface JsonSchema {
+  type: string;
+  properties?: Record<string, unknown>;
+  items?: unknown;
+  required?: string[];
+  additionalProperties?: boolean;
+}
+
+export function cardOutputSchema(strict: boolean): JsonSchema {
+  const cardSchema: JsonSchema = {
     type: 'object',
     properties: {
       title: { type: 'string' },
@@ -119,7 +127,7 @@ export function cardOutputSchema(strict: boolean) {
     },
     required: ['title', 'anchor', 'gist', 'bullets'],
   };
-  const rootSchema: any = {
+  const rootSchema: JsonSchema = {
     type: 'object',
     properties: {
       cards: {