fix(deploy): a permanent upload outage, a dead-on-arrival Caddy, and 11pm commands that don't run

* Caddy had no read_body, on the reasoning that "a slow body still has to
  actually send bytes". That is an argument about disk, and disk is not the
  scarce resource: upload_admission budgets concurrent bodies at 4096 MiB and
  reserves the DECLARED cap, so a video/* upload reserves 500 MiB. Eight
  connections that stall mid-body hold the whole budget, every other guest
  waits 20s and gets a 503, and it never recovers on its own — the permit is
  held until the handler returns. No attacker needed: eight guests starting
  real videos and walking out of AP range does it, and TCP will not reap
  those sockets for hours. 30m carries a 500 MB upload at ~2.2 Mbit/s, so it
  does not fail the uploads this product exists to collect.

* APP_PORT is presented in .env.example as an ordinary editable line, while
  the healthcheck hardcodes 127.0.0.1:3000 and the Caddyfile hardcodes
  app:3000. Change it and the app boots and serves happily on the new port,
  the healthcheck fails forever, app never turns healthy — and because caddy
  is gated on service_healthy, CADDY NEVER STARTS. Port 443 dead for the
  whole event, sole diagnostic "dependency failed to start". Pinned in
  compose beside MEDIA_PATH and EXPORT_PATH, which are there for this reason.

* Runbook §12's recovery commands do not run as written: unwrapped
  "$POSTGRES_USER" is expanded by the operator's shell, which does not have
  it, so psql answers `FATAL: role "" does not exist`. §9 documents that trap
  two hundred lines earlier and wraps its own calls in sh -c; §12 did not.
  This is the block you run with the app crash-looping behind a live Caddy.
  Its DELETE also hard-coded versions 21,22,23 as if to be copied verbatim,
  on a tree that now has 31 migrations — now explicitly an example, with the
  instruction to take the numbers from the actual boot error.

* Migration counts corrected across the runbook and .env.example (22 -> 31,
  commit count 154 -> 196). All four were presented as literal command output
  the operator is invited to reproduce.

docker-compose.yml

@@ -104,6 +104,14 @@ services:
       # create it and every upload 500s with EACCES. `environment` overrides `env_file`,
       # so this is authoritative for the container.
       MEDIA_PATH: /media
+      # Third member of the MEDIA_PATH / EXPORT_PATH family, and the nastiest of the three because
+      # the app itself reports nothing wrong. The healthcheck below hardcodes 127.0.0.1:3000 and
+      # the Caddyfile hardcodes app:3000, while `.env.example` presents APP_PORT as an ordinary
+      # editable line. Change it there and the app boots and serves happily on the new port, the
+      # healthcheck fails forever, `app` never turns healthy — and because caddy is gated on
+      # `service_healthy`, CADDY NEVER STARTS AT ALL. Port 443 is dead for the whole event and the
+      # only diagnostic is `dependency failed to start`.
+      APP_PORT: "3000"
       # Pinned for the same reason as MEDIA_PATH: `environment` beats `env_file`, so this cannot
       # be lost by an operator who copies `.env.example` and edits only the secrets — which is
       # the likely path, and `.env.example` ships the generic default of `true`.