feat(mods): replace packwiz with distribution-fed custom mod volume

Drop packwiz entirely. The server now loads a filtered mod subset from a
local ./server-mods volume instead of fetching a packwiz pack at boot.

New flow:
- tooling/classify-mods.py (tomllib only, no network) reads each jar's
  META-INF/neoforge.mods.toml and seeds mods-sides.json with a side
  (client|server|both; default both). Existing entries are preserved.
- mods-sides.json: committed, keyed by jar filename, hand-editable override
  surface. Initial seed: 65 both, 11 client, 0 server (76 jars).
- tooling/sync-server-mods.sh mirrors the both/server jars from
  $DISTRIBUTION_WEB_ROOT into ./server-mods/ (authoritative; prunes strays;
  halts on a missing jar). Replaces render-pack.sh.
- compose: minecraft mounts ./server-mods:/mods:ro with REMOVE_OLD_MODS=TRUE
  (itzg auto-syncs /mods -> /data/mods). Removed PACKWIZ_URL, the pack.
  extra_host (auth. kept for authlib), and depends_on caddy (drasl kept).

Both classify-mods.py and sync-server-mods.sh resolve their source dir as:
CLI arg / MODS_DIST_DIR env / $DISTRIBUTION_WEB_ROOT (in that order).

Removed: tooling/render-pack.sh + add-custom-mod.sh (packwiz tooling),
pack/ (packwiz source), custom/ (76 jars now sourced from the distribution),
the pack. caddy vhost + its mounts/alias, and the packwiz .gitignore block.

Client distribution is UNCHANGED: HeliosLauncher still installs the full
modset from distribution.json. Docs (CLAUDE.md, plan/04/05/14, runtime)
updated; plan/04-packwiz.md stubbed as superseded by plan/04-mods.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -6,15 +6,13 @@ runtime/authlib-injector.jar
 # rendered configs (from tooling/render-config.sh)
 drasl/config/config.toml
 nmsr/config.toml
-# packwiz pack files rendered from pack/**/*.tmpl by tooling/render-pack.sh
-# (domain-dependent build output); source of truth is the .tmpl + custom/ jars.
-pack/mods/*.pw.toml
-pack/index.toml
-pack/CustomSkinLoader/CustomSkinLoader.json
+
+# server mod subset synced from the distribution repo by
+# tooling/sync-server-mods.sh (source of truth is mods-sides.json + $DIST jars)
+server-mods/
 
 # vendored binaries
 launcher/
-pack/mods-files/
 
 # landing page: generated build output + deps
 www/