fix: use debian:trixie-slim runtime to match builder glibc 2.38

rust:1.95-slim is trixie-based (glibc 2.38); bookworm-slim only has
2.36, causing a crash on startup.

Dockerfile

@@ -10,7 +10,7 @@ RUN pnpm run check
 RUN pnpm run build
 
 # --- Backend Build ---
-FROM rust:1.95-slim AS backend-builder
+FROM rust:1.95-slim-bookworm AS backend-builder
 WORKDIR /app/backend
 COPY backend/Cargo.toml backend/Cargo.lock ./
 RUN mkdir src && echo "fn main() {}" > src/main.rs && cargo build --release && rm -rf src
@@ -20,7 +20,7 @@ COPY backend/demo ./demo
 RUN touch src/main.rs && cargo build --release
 
 # --- Runtime ---
-FROM debian:bookworm-slim
+FROM debian:trixie-slim
 RUN apt-get update && apt-get install -y ca-certificates curl && rm -rf /var/lib/apt/lists/*
 RUN useradd -u 1000 -m app
 WORKDIR /app