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updated; plan/04-packwiz.md stubbed as superseded by plan/04-mods.md.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>

caddy/Caddyfile

@@ -1,5 +1,5 @@
 # Base Caddy config. Vhosts live in conf.d/*.caddy snippets:
-#   conf.d/00-core.caddy          auth + packwiz
+#   conf.d/00-core.caddy          auth
 #   conf.d/10-static.caddy        apex landing + launcher downloads
 #   conf.d/30-distribution.caddy  static site from another repo
 #   conf.d/40-avatar.caddy        nmsr skin/avatar renderer

caddy/conf.d/00-core.caddy

@@ -1,9 +1,4 @@
-# Core ingress — always mounted. Drasl auth + packwiz pack metadata.
+# Core ingress — always mounted. Drasl auth.
 http://auth.{$BASE_DOMAIN} {
 	reverse_proxy drasl:25585
 }
-
-http://pack.{$BASE_DOMAIN} {
-	root * /srv/pack
-	file_server browse
-}