feat(FN-207): Step 1 — add downgradeOffer i18n keys (tr + en) (+4 more)

Commits merged:
- style(FN-207): apply Biome formatting
- feat(FN-207): Steps 4-9 — add downgrade save-flow UI (helper, dialogs, plans query, handler)
- feat(FN-207): Step 3 — add PATCH /subscriptions/downgrade and GET /subscriptions/plans endpoints
- feat(FN-207): Step 2 — add downgrade() and getPlans() service methods
- feat(FN-207): Step 1 — add downgradeOffer i18n keys (tr + en)

Files changed:
.../src/subscriptions/subscriptions.controller.ts  |  13 ++
 .../api/src/subscriptions/subscriptions.service.ts |  75 ++++++
 apps/web/src/messages/en.json                      |  10 +
 apps/web/src/messages/tr.json                      |  10 +
 apps/web/src/routes/dashboard/index.tsx            |  16 +-
 .../src/routes/dashboard/subscription/index.tsx    | 255 ++++++++++++++++++---
 6 files changed, 340 insertions(+), 39 deletions(-)

Fusion-Task-Id: FN-207

apps/api/src/subscriptions/subscriptions.controller.ts

@@ -49,6 +49,19 @@ export class SubscriptionsController {
     return this.subscriptionsService.resume(userId);
   }
 
+  @Patch("downgrade")
+  async downgrade(
+    @CurrentUser("id") userId: string,
+    @Body() body: { planId: string; brandIds: string[] },
+  ) {
+    return this.subscriptionsService.downgrade(userId, body);
+  }
+
+  @Get("plans")
+  async getPlans() {
+    return this.subscriptionsService.getPlans();
+  }
+
   @Get()
   @UseGuards(RolesGuard)
   @Roles("admin")

apps/api/src/subscriptions/subscriptions.service.ts

@@ -308,6 +308,81 @@ export class SubscriptionsService {
     return subscription;
   }
 
+  async downgrade(userId: string, data: { planId: string; brandIds: string[] }) {
+    // Find active subscription
+    const [sub] = await this.db
+      .select()
+      .from(userSubscriptions)
+      .where(and(eq(userSubscriptions.userId, userId), eq(userSubscriptions.status, "active")))
+      .limit(1);
+
+    if (!sub) throw new NotFoundException("Aktif abonelik bulunamadı");
+
+    // Validate target plan exists
+    const [targetPlan] = await this.db
+      .select()
+      .from(plans)
+      .where(eq(plans.id, data.planId))
+      .limit(1);
+
+    if (!targetPlan) throw new NotFoundException("Plan bulunamadı");
+
+    // Validate brand count matches plan
+    if (targetPlan.brandCount > 0 && data.brandIds.length !== targetPlan.brandCount) {
+      throw new BadRequestException(`Bu plan tam olarak ${targetPlan.brandCount} marka gerektirir`);
+    }
+
+    // Update subscription plan
+    const [updated] = await this.db
+      .update(userSubscriptions)
+      .set({ planId: data.planId, updatedAt: new Date() })
+      .where(eq(userSubscriptions.id, sub.id))
+      .returning();
+
+    // Replace brand associations
+    await this.db.delete(userBrands).where(eq(userBrands.subscriptionId, sub.id));
+
+    if (data.brandIds.length > 0) {
+      await this.db.insert(userBrands).values(
+        data.brandIds.map((brandId) => ({
+          userId,
+          subscriptionId: sub.id,
+          brandId,
+        })),
+      );
+    }
+
+    return updated;
+  }
+
+  async getPlans() {
+    const rows = await this.db
+      .select({
+        id: plans.id,
+        name: plans.name,
+        brandCount: plans.brandCount,
+        priceMonthly: plans.priceMonthly,
+        priceYearly: plans.priceYearly,
+      })
+      .from(plans)
+      .where(eq(plans.isActive, true));
+
+    // Map DB name to frontend key
+    const nameToKey: Record<string, string> = {
+      "1 Marka": "brand1",
+      "2 Marka": "brand2",
+      "3 Marka": "brand3",
+      "Full Paket": "full",
+    };
+
+    return rows
+      .filter((p) => nameToKey[p.name])
+      .map((p) => ({
+        ...p,
+        key: nameToKey[p.name],
+      }));
+  }
+
   async findAll(page = 1, limit = 20) {
     const offset = (page - 1) * limit;
     const items = await this.db