feat(engine): merge cloudflare-migration — paradigm D engine, BYOK proxy, story persistence (#95)

Squash-merge the cloudflare-migration branch (7 commits by Kai ki) into
staging with conflict resolution, feature integration, and bug fixes.

Engine:
- Paradigm D: single-stream Writer replacing dual-phase Plan/Beats
- Delete Architect agent; story bible generated via Writer <plan> tag
- Modular prompt architecture (segments/registry/builder)
- StreamRouter for tagged stream splitting (<plan>/<story>/<choices>)

Infrastructure:
- Cloudflare Workers deployment (wrangler.jsonc, OpenNext adapter)
- D1 database schema + Drizzle ORM (scaffolded, not yet active)
- R2 storage helpers (scaffolded, not yet active)
- Story persistence API routes + client-side persistence

BYOK (Bring Your Own Key):
- /api/llm/user-proxy with SSRF-protected LLM proxy (+ requireUser auth)
- CORS-aware fetch in ai-client: auto-detect CORS failure, fallback to
  server proxy transparently via OpenAI SDK custom fetch
- BYO config support added to classify-freeform and vision routes
- SettingsModal CORS privacy notice (keys never logged/stored)

SSE streaming:
- engineClient.ts: fetchSSE helper for progressive scene events
- startSession/requestScene accept optional emit callback
- Fix SSE error event field name (error → message) in scene/start routes

i18n integration:
- Wire buildLanguageDirective into paradigm D's prompt builder
- Update corsNotice i18n keys (zh-CN/en/ja) with CORS proxy privacy text
- Preserve Session.language + LanguageSwitcher from i18n commit

Co-authored-by: Kai ki <155355644+zbf1009@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

lib/db/repositories/featuredRepo.ts

@@ -0,0 +1,45 @@
+import "server-only";
+
+import { eq, and, sql } from "drizzle-orm";
+import type { DbInstance } from "../client";
+import { featuredStories } from "../schema";
+import type { FeaturedStory } from "../schema";
+
+/**
+ * Featured Story Repository - encapsulates D1 access for homepage featured stories.
+ *
+ * Provides: listByGender (active only, sorted by sortOrder), incrementClick (analytics).
+ */
+export class FeaturedRepository {
+  constructor(private db: DbInstance) {}
+
+  /**
+   * List active featured stories for a given gender, ordered by sortOrder.
+   *
+   * @param gender "male" or "female"
+   * @returns Array of FeaturedStory (only isActive=1, sorted by sortOrder ASC)
+   */
+  async listByGender(gender: "male" | "female"): Promise<FeaturedStory[]> {
+    return this.db
+      .select()
+      .from(featuredStories)
+      .where(and(eq(featuredStories.gender, gender), eq(featuredStories.isActive, 1)))
+      .orderBy(featuredStories.sortOrder);
+  }
+
+  /**
+   * Increment click count for a featured story (analytics).
+   *
+   * @param id Featured story ID (e.g. "m0", "f12")
+   * @returns true if updated, false if not found
+   */
+  async incrementClick(id: string): Promise<boolean> {
+    const result = await this.db
+      .update(featuredStories)
+      .set({ clickCount: sql`${featuredStories.clickCount} + 1` })
+      .where(eq(featuredStories.id, id));
+
+    // Drizzle D1 update returns { success, meta: { changes }, results }
+    return ((result as any).meta?.changes ?? 0) > 0;
+  }
+}