Start av-club: what it is, and a verified installer

Media processing pulled out of the website that first needed it. ffmpeg,
ImageMagick, libvips and exiftool are a real installation rather than an npm
install, and encoder settings get revisited as browser support moves — neither of
which belongs on the same clock as page templates and database schemas.

No processing code yet. What is here is the tooling requirement, an installer, and
docs/PIPELINE.md writing down what has NOT been decided — how a consumer talks to
this, whether processing blocks an upload, where output goes — so those get chosen
deliberately instead of by whatever gets written first.

verify.sh checks by running: it encodes a video and probes the result against what
ffmpeg was told to make, loads sharp under Bun specifically, and asserts a
re-encode still strips GPS. That last one guards a real leak — if a future sharp
changes its default, this fails a check rather than quietly publishing the
coordinates of a client's living room. Confirmed non-vacuous by hiding ffmpeg and
watching it exit 1.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,15 @@
+node_modules
+dist
+*.tgz
+coverage
+*.log
+.cache
+*.tsbuildinfo
+.idea
+.DS_Store
+
+.env
+.env.local
+
+# scratch space for trying things against real files
+tmp/