feat: add unlimited option to tier limits

Use -1 as a sentinel meaning "no cap" in tier_definitions numeric
columns. checkAndIncrementTierLimit skips the usage-cap WHERE clause
when the limit is -1. Admin tier UI gets an Unlimited switch per
field that disables the input and sends -1.

apps/web/lib/tiers.ts

@@ -9,6 +9,9 @@ function currentMonth() {
 
 export type LimitKey = "recipe" | "aiCall" | "storage";
 
+/** Sentinel stored in tier_definitions numeric columns to mean "no cap". */
+export const UNLIMITED = -1;
+
 export class TierLimitError extends Error {
   constructor(public readonly limit: LimitKey, public readonly tier: string) {
     super(`Tier limit reached: ${limit} (tier: ${tier})`);
@@ -42,12 +45,13 @@ export async function checkAndIncrementTierLimit(
 
   if (key === "aiCall") {
     const limit = tierDef.aiCallsPerMonth;
+    const cap = limit === UNLIMITED ? sql`true` : sql`user_usage.ai_calls_used < ${limit}`;
     const result = await db.execute(sql`
       INSERT INTO user_usage (id, user_id, month, ai_calls_used, recipe_count, storage_used_mb)
       VALUES (${id}, ${userId}, ${month}, 1, 0, 0)
       ON CONFLICT (user_id, month) DO UPDATE
         SET ai_calls_used = user_usage.ai_calls_used + 1
-        WHERE user_usage.ai_calls_used < ${limit}
+        WHERE ${cap}
       RETURNING ai_calls_used
     `);
     if (result.length === 0) {
@@ -55,12 +59,13 @@ export async function checkAndIncrementTierLimit(
     }
   } else {
     const limit = tierDef.maxRecipes;
+    const cap = limit === UNLIMITED ? sql`true` : sql`user_usage.recipe_count < ${limit}`;
     const result = await db.execute(sql`
       INSERT INTO user_usage (id, user_id, month, ai_calls_used, recipe_count, storage_used_mb)
       VALUES (${id}, ${userId}, ${month}, 0, 1, 0)
       ON CONFLICT (user_id, month) DO UPDATE
         SET recipe_count = user_usage.recipe_count + 1
-        WHERE user_usage.recipe_count < ${limit}
+        WHERE ${cap}
       RETURNING recipe_count
     `);
     if (result.length === 0) {