fix: install every tool the e2e fixtures need, not just the first one

The previous commit added ffmpeg and exiftool and CI got exactly one step
further before failing on `heif-enc: No such file or directory`. Fixing a
missing dependency one CI run at a time is a guess repeated; the list comes
from the source instead -- every argv[0] handed to run_tool in
tool/e2e_fixtures.py is ffmpeg, exiftool and heif-enc, and heif-enc ships in
libheif-examples on Ubuntu.

Each binary is resolved after the install rather than the apt exit code
being taken as the claim, so a package that renames its binary fails here
with a message naming it instead of failing later inside a fixture builder.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01416TegJ3sa8xL5qGGgrygP

.github/workflows/ci.yml

@@ -21,12 +21,22 @@ jobs:
       # and MP4 fixtures with ffmpeg, and signal_bot/media_strip.py strips
       # metadata with exiftool. Verified rather than trusted, because an
       # apt exit code is not the same claim as "the binary resolves".
-      - name: Install ffmpeg and exiftool
+      # Every binary tool/e2e_fixtures.py shells out to, which is the whole
+      # list rather than the first one that failed: ffmpeg builds the JPEG
+      # and MP4 fixtures, heif-enc the HEIC one, and exiftool is what
+      # signal_bot/media_strip.py strips metadata with. scripts/e2e.sh has
+      # needed all three since it was written and this file installed none of
+      # them, which is why CI has been red on every commit.
+      #
+      # Verified by resolving each binary, not by trusting apt's exit code --
+      # the same distinction install_service.sh makes for the host.
+      - name: Install the tools the fixtures are built with
         run: |
           sudo apt-get update
-          sudo apt-get install -y ffmpeg libimage-exiftool-perl
-          ffmpeg -version | head -1
-          exiftool -ver
+          sudo apt-get install -y ffmpeg libimage-exiftool-perl libheif-examples
+          for tool in ffmpeg exiftool heif-enc; do
+            command -v "$tool" || { echo "::error::$tool did not resolve"; exit 1; }
+          done
 
       - name: Install uv
         uses: astral-sh/setup-uv@v5