feat: add conditional asset embedding with dev/prod build separation

- Add embed-assets feature flag to make rust-embed/mime_guess optional
- Update Justfile with backend-dev command for development (no embedded assets)
- Add CORS middleware when assets not embedded (for Vite proxy)
- Improve db recipe with Bun script supporting start/reset/rm commands

Justfile

@@ -22,36 +22,72 @@ format-check:
     bun run --cwd web format:check
 
 # Start PostgreSQL in Docker and update .env with connection string
-db:
-    #!/usr/bin/env bash
-    set -euo pipefail
+# Commands: start (default), reset, rm
+[script("bun")]
+db cmd="start":
+    const fs = await import("fs/promises");
+    const { spawnSync } = await import("child_process");
 
-    # Find available port
-    PORT=$(shuf -i 49152-65535 -n 1)
-    while ss -tlnp 2>/dev/null | grep -q ":$PORT "; do
-        PORT=$(shuf -i 49152-65535 -n 1)
-    done
+    const NAME = "banner-postgres";
+    const USER = "banner";
+    const PASS = "banner";
+    const DB = "banner";
+    const PORT = "59489";
+    const ENV_FILE = ".env";
+    const CMD = "{{cmd}}";
 
-    # Start PostgreSQL container
-    docker run -d \
-        --name banner-postgres \
-        -e POSTGRES_PASSWORD=banner \
-        -e POSTGRES_USER=banner \
-        -e POSTGRES_DB=banner \
-        -p "$PORT:5432" \
-        postgres:17-alpine
+    const run = (args) => spawnSync("docker", args, { encoding: "utf8" });
+    const getContainer = () => {
+      const res = run(["ps", "-a", "--filter", `name=^${NAME}$`, "--format", "json"]);
+      return res.stdout.trim() ? JSON.parse(res.stdout) : null;
+    };
 
-    # Update .env file
-    DB_URL="postgresql://banner:banner@localhost:$PORT/banner"
-    if [ -f .env ]; then
-        sed -i.bak "s|^DATABASE_URL=.*|DATABASE_URL=$DB_URL|" .env
-    else
-        echo "DATABASE_URL=$DB_URL" > .env
-    fi
+    const updateEnv = async () => {
+      const url = `postgresql://${USER}:${PASS}@localhost:${PORT}/${DB}`;
+      try {
+        let content = await fs.readFile(ENV_FILE, "utf8");
+        content = content.includes("DATABASE_URL=")
+          ? content.replace(/DATABASE_URL=.*$/m, `DATABASE_URL=${url}`)
+          : content.trim() + `\nDATABASE_URL=${url}\n`;
+        await fs.writeFile(ENV_FILE, content);
+      } catch {
+        await fs.writeFile(ENV_FILE, `DATABASE_URL=${url}\n`);
+      }
+    };
 
-    echo "PostgreSQL started on port $PORT"
-    echo "DATABASE_URL=$DB_URL"
-    echo "Run: sqlx migrate run"
+    const create = () => {
+      run(["run", "-d", "--name", NAME, "-e", `POSTGRES_USER=${USER}`,
+           "-e", `POSTGRES_PASSWORD=${PASS}`, "-e", `POSTGRES_DB=${DB}`,
+           "-p", `${PORT}:5432`, "postgres:17-alpine"]);
+      console.log("created");
+    };
+
+    const container = getContainer();
+
+    if (CMD === "rm") {
+      if (!container) process.exit(0);
+      run(["stop", NAME]);
+      run(["rm", NAME]);
+      console.log("removed");
+    } else if (CMD === "reset") {
+      if (!container) create();
+      else {
+        run(["exec", NAME, "psql", "-U", USER, "-d", "postgres", "-c", `DROP DATABASE IF EXISTS ${DB}`]);
+        run(["exec", NAME, "psql", "-U", USER, "-d", "postgres", "-c", `CREATE DATABASE ${DB}`]);
+        console.log("reset");
+      }
+      await updateEnv();
+    } else {
+      if (!container) {
+        create();
+      } else if (container.State !== "running") {
+        run(["start", NAME]);
+        console.log("started");
+      } else {
+        console.log("running");
+      }
+      await updateEnv();
+    }
 
 # Auto-reloading frontend server
 frontend:
@@ -61,10 +97,14 @@ frontend:
 build-frontend:
     bun run --cwd web build
 
-# Auto-reloading backend server
+# Auto-reloading backend server (with embedded assets)
 backend *ARGS:
     bacon --headless run -- -- {{ARGS}}
 
+# Auto-reloading backend server (no embedded assets, for dev proxy mode)
+backend-dev *ARGS:
+    bacon --headless run -- --no-default-features -- {{ARGS}}
+
 # Production build
 build:
     bun run --cwd web build
@@ -74,6 +114,6 @@ build:
 dev-build *ARGS='--services web --tracing pretty': build-frontend
     bacon --headless run -- --profile dev-release -- {{ARGS}}
 
-# Auto-reloading development build for both frontend and backend
+# Auto-reloading development build: Vite frontend + backend (no embedded assets, proxies to Vite)
 [parallel]
-dev *ARGS='--services web,bot': frontend (backend ARGS)
+dev *ARGS='--services web,bot': frontend (backend-dev ARGS)