Build the container on Debian trixie for ffmpeg 7.1 (#177)

Bookworm's ffmpeg is 5.1.9, two major versions behind, and DeadAir runs
everything through it. Both stages move, since the binary built in the
first has to find the same glibc in the second.

Checked in the new image on techpod-358 with a 643-term drop expression,
the size that failed with a bsf_list error on 5.1 today: the copy is
352.73s shorter, as 643 cuts of 21 frames at 26.122ms predict, and
decodes without errors.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Dockerfile

@@ -1,7 +1,7 @@
 # Build. rusqlite is bundled (compiles SQLite from source) and librqbit needs a C
 # toolchain, so the builder needs cc. TLS is rustls throughout, so no OpenSSL headers.
 # build.rs builds the web pages from TypeScript with swc, which needs node.
-FROM rust:1-slim-bookworm AS build
+FROM rust:1-slim-trixie AS build
 RUN apt-get update && apt-get install -y --no-install-recommends \
         build-essential nodejs npm \
     && rm -rf /var/lib/apt/lists/*
@@ -23,7 +23,7 @@ COPY web ./web
 # cargo skips a rebuild if mtimes look untouched; make sure it does not.
 RUN touch src/main.rs && cargo build --release --locked
 
-FROM debian:bookworm-slim
+FROM debian:trixie-slim
 # ffmpeg is DeadAir's (#171): it finds the silences and copies the frames kept. Debian's adds
 # about 480 MB, once: the layer stays cached until the base image changes.
 RUN apt-get update && apt-get install -y --no-install-recommends \