refactor (v2): better arch

Co-authored-by: Copilot <copilot@github.com>

.env.example

@@ -0,0 +1,48 @@
+# ── Required ──────────────────────────────────────────────────────────────────
+
+# SQLite database path
+DATABASE_URL=sqlite:data.db?mode=rwc
+
+# JWT signing secret — change this before deploying
+# Generate a strong one: openssl rand -hex 32
+JWT_SECRET=change-me-before-deploying-use-openssl-rand-hex-32
+
+# ── Server ────────────────────────────────────────────────────────────────────
+
+HOST=0.0.0.0
+PORT=3000
+
+# Comma-separated allowed CORS origins (empty = block all cross-origin requests)
+CORS_ORIGINS=http://localhost:5173
+
+# Set to false to disable public registration
+ALLOW_REGISTRATION=true
+
+# ── Events ────────────────────────────────────────────────────────────────────
+
+# If unset, an in-memory bus is used (fine for single-process dev).
+# For the worker to process note events, set this.
+# NATS_URL=nats://localhost:4222
+
+# ── Smart features (optional) ─────────────────────────────────────────────────
+
+# Set both to enable semantic search and related notes.
+# QDRANT_URL=http://localhost:6334
+# QDRANT_COLLECTION=notes
+
+# Set to true ONLY in the worker process — loads the fastembed model (~150 MB).
+# Leave unset (or false) in the API server.
+# ENABLE_EMBEDDINGS=true
+
+# ── Frontend ──────────────────────────────────────────────────────────────────
+
+# Path to the built SPA dist directory.
+# Defaults to k-notes-frontend/dist (run `make build-frontend` first).
+# Set to empty string to run API-only (no SPA served).
+# SPA_DIR=k-notes-frontend/dist
+
+# ── JWT options (optional) ────────────────────────────────────────────────────
+
+# JWT_EXPIRY_HOURS=24
+# JWT_ISSUER=
+# JWT_AUDIENCE=