docs: add architecture diagrams (D2 + Mermaid)

Adds docs/architecture.d2 and docs/architecture.mermaid.md showing the
docker-compose-new.yml service topology — storage, application, init
containers, and external dependencies with annotated connections.

Also includes the rendered docs/architecture.svg (D2 output).

View live: d2 --watch docs/architecture.d2
View in Gitea: navigate to docs/architecture.mermaid.md in the web UI.

docs/architecture.d2

@@ -0,0 +1,99 @@
+direction: right
+
+# ─── External ─────────────────────────────────────────────────────────────────
+
+novelfire: novelfire.net {
+  shape: cloud
+  style.fill: "#f0f4ff"
+}
+
+kokoro: Kokoro-FastAPI TTS {
+  shape: cloud
+  style.fill: "#f0f4ff"
+}
+
+browser: Browser / iOS App {
+  shape: person
+  style.fill: "#fff9e6"
+}
+
+# ─── Init containers (one-shot) ───────────────────────────────────────────────
+
+init: Init containers {
+  style.fill: "#f5f5f5"
+  style.stroke-dash: 4
+
+  minio-init: minio-init {
+    shape: rectangle
+    label: "minio-init\n(mc: create buckets)"
+  }
+
+  pb-init: pb-init {
+    shape: rectangle
+    label: "pb-init\n(bootstrap collections)"
+  }
+}
+
+# ─── Storage ──────────────────────────────────────────────────────────────────
+
+storage: Storage {
+  style.fill: "#eaf7ea"
+
+  minio: MinIO {
+    shape: cylinder
+    label: "MinIO :9000\n\nbuckets:\n  libnovel-chapters\n  libnovel-audio\n  libnovel-avatars\n  libnovel-browse"
+  }
+
+  pocketbase: PocketBase {
+    shape: cylinder
+    label: "PocketBase :8090\n\ncollections:\n  books  chapters_idx\n  audio_cache  progress\n  scrape_jobs  app_users\n  ranking"
+  }
+}
+
+# ─── Application ──────────────────────────────────────────────────────────────
+
+app: Application {
+  style.fill: "#eef3ff"
+
+  backend: backend {
+    shape: rectangle
+    label: "Backend API :8080\n(Go — HTTP API server)"
+  }
+
+  runner: runner {
+    shape: rectangle
+    label: "Runner\n(Go — background worker\nscraping + TTS jobs)"
+  }
+
+  ui: ui {
+    shape: rectangle
+    label: "SvelteKit UI :5252\n(adapter-node)"
+  }
+}
+
+# ─── Init → Storage deps ──────────────────────────────────────────────────────
+
+init.minio-init -> storage.minio: create buckets {style.stroke-dash: 4}
+init.pb-init -> storage.pocketbase: bootstrap schema {style.stroke-dash: 4}
+
+# ─── App → Storage ────────────────────────────────────────────────────────────
+
+app.backend -> storage.minio: blobs (chapters, audio,\navatars, browse)
+app.backend -> storage.pocketbase: structured records\n(books, progress, jobs…)
+
+app.runner -> storage.minio: write chapter markdown\n& audio MP3s
+app.runner -> storage.pocketbase: read/update scrape jobs\nwrite book records
+
+# ─── App internal ─────────────────────────────────────────────────────────────
+
+app.ui -> app.backend: REST API calls\n(server-side)
+
+# ─── External → App ───────────────────────────────────────────────────────────
+
+app.runner -> novelfire: scrape\n(HTTP GET)
+app.runner -> kokoro: TTS generation\n(HTTP POST)
+
+# ─── Browser ──────────────────────────────────────────────────────────────────
+
+browser -> app.ui: HTTPS :5252
+browser -> storage.minio: presigned URLs\n(audio / chapter downloads)