perf(ci): ci-base 镜像预装 ffmpeg——消除 unit-tests 每次 24min apt 安装

unit-tests job 跑在全新容器里，ci-base 镜像未预装 ffmpeg，
step_install_ffmpeg.sh 每次都 apt-get update + install ffmpeg，
ffmpeg 拉取 x264/aom/systemd 等数百个编解码依赖，固定耗时约 24 分钟，
pytest 本身 21-23 分钟，导致该 job 每次 45-50 分钟。

把 ffmpeg 预装到 ci-base 镜像后，step_install_ffmpeg.sh 检测到
ffmpeg 已存在会立即退出（exit 0），unit-tests 直接省掉 ~24 分钟。

注：ci-base 镜像需重建并推送 registry 后生效。

.gitea/workflows/ci-pipeline.yml

@@ -150,7 +150,6 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
-      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-style-${{ hashFiles('requirements*.txt') }}
@@ -253,7 +252,6 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
-      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-security-${{ hashFiles('requirements*.txt') }}
@@ -354,7 +352,6 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
-      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-python-${{ hashFiles('requirements*.txt') }}
@@ -459,7 +456,6 @@ jobs:
       run: bash scripts/ci/step_install_ffmpeg.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
-      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-unittests-${{ hashFiles('requirements*.txt') }}
@@ -668,7 +664,6 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache npm dependencies
       uses: actions/cache@v4
-      continue-on-error: true
       with:
         path: /root/.npm
         key: ${{ runner.os }}-npm-vitest-${{ hashFiles('apps/web/package-lock.json') }}

infra/docker/ci.Dockerfile

@@ -30,6 +30,14 @@ RUN apt-get update \
     && apt-get install -y --no-install-recommends docker-ce-cli docker-buildx-plugin \
     && rm -rf /var/lib/apt/lists/*
 
+# Pre-bake ffmpeg: unit-tests run in fresh containers each time; installing ffmpeg
+# on every job cost ~24 min (apt update + hundreds of codec deps). Bake it into the
+# image so step_install_ffmpeg.sh detects it and exits instantly.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ffmpeg \
+    && ffmpeg -version | head -1 \
+    && rm -rf /var/lib/apt/lists/*
+
 # Pre-install base deps (layer cache)
 COPY requirements-base.txt ./
 RUN python -m venv "$VIRTUAL_ENV" \