feat(modules): mount the modules directory as a volume (phase 2, PR 9)

Closes Phase 2. Modules live on a mount, never in the image — that is what
lets an operator add one to a pull-only deployment without building anything.

`./modules` is a bind mount rather than a named volume: placing a module
directory by hand is a supported install (MODULE_SYSTEM.md §2.5), and that has
to be doable from the host rather than through `docker cp`. Read-write, because
the admin panel's install/uninstall unpacks and removes directories there.

The directory is tracked via its README so it exists in the checkout with the
operator's own ownership — Docker recreates a missing bind-mount source as
root:root, which the container user could not then write. `.dockerignore`
excludes it so a module in the builder's working tree can never ship inside an
image.

Also corrects the route-manifest generator's list of filesystem-conditional
mounts, which never picked up `/modules` when PR 7 added it. Comment only; the
generator filters on an allowlist, so its behaviour was already right.

Verified against a real container, not just a parsed compose file: image
carries an empty node-owned /app/modules despite a module in the build context;
a module on the bind mount loads, mounts, replays and reaches `started`;
`/api/v1/public/modules` lists it; the chunk serves from the entry's directory
only (server source and module.json 404) with `no-cache`; the injected tag
follows core's bundle; and in Chrome the page renders on first paint inside
core's PublicLayout with its nav row interleaved into core's public nav, under
enforced `script-src 'self'` with zero CSP reports and no console errors.
Removing the directory by hand reconciles the row to `startup_failed`/`require`
and leaves core healthy with no injection.

933 server + 160 client tests pass, manifest unchanged at 230 routes, swagger
regenerates byte-identical.

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

.gitignore

@@ -21,6 +21,13 @@ uploads/
 server/logs/
 logs/
 
+# Installed modules (docs/website/MODULE_SYSTEM.md). Core ships no module, so
+# anything here is an operator's install or a developer's scratch copy. The
+# directory itself IS tracked, via its README: docker-compose.yml bind-mounts it,
+# and a missing bind-mount source is recreated by Docker as root-owned.
+modules/*
+!modules/README.md
+
 # Operator-supplied spawn atlas artwork. Creature art is never committed: sprites
 # are extracted from the operator's own UO client .mul/.uop files and are theirs,
 # not ours to redistribute. The images live under server/uploads/atlas/, already