fix(left4me): move ProcSubset=pid from COMMON to SERVER-only

Discovered post-deploy: ProcSubset=pid hides /proc/sys/kernel/random/boot_id
which journalctl reads at startup. The web app invokes
`sudo -n left4me-journalctl` to stream live server logs into the UI;
journalctl bails with "Failed to get boot ID" before producing any
output. Web log streaming was silently broken.

Server unit keeps ProcSubset=pid (srcds doesn't invoke journalctl);
web unit drops it. ProtectProc=invisible remains in COMMON — that's
the load-bearing D4 defense (foreign-uid /proc hidden).

Reproducer that confirms the diagnosis:
  systemd-run --pipe --uid=left4me --gid=left4me \
    -p ProcSubset=pid -p ProtectProc=invisible \
    -p ProtectSystem=strict -p PrivateTmp=true \
    [...rest of web hardening...] \
    -- sh -c 'sudo -n left4me-journalctl 2 --lines 3 --follow >/var/lib/left4me/tmp/out 2>&1'
  # cat /var/lib/left4me/tmp/out → "Failed to get boot ID: No such file or directory"
  # rc → 1
With ProcSubset=all: timeout 124 (helper running), 3 lines streamed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

bundles/left4me/metadata.py

@@ -128,9 +128,14 @@ defaults = {
 # (paths in the left4me repo)
 
 # Directives both managed units take verbatim.
+#
+# ProcSubset=pid is intentionally NOT in COMMON: it hides
+# /proc/sys/kernel/random/boot_id which journalctl reads at startup,
+# and the web unit invokes `sudo -n left4me-journalctl ...` to stream
+# live server logs into the UI. Server unit adds it back in
+# HARDENING_SERVER (srcds doesn't read journalctl).
 HARDENING_COMMON = {
     'ProtectProc': 'invisible',
-    'ProcSubset': 'pid',
     'ProtectKernelTunables': 'true',
     'ProtectKernelModules': 'true',
     'ProtectKernelLogs': 'true',
@@ -154,6 +159,7 @@ HARDENING_COMMON = {
 # socket binds.
 HARDENING_SERVER = {
     **HARDENING_COMMON,
+    'ProcSubset': 'pid',
     'NoNewPrivileges': 'true',
     'RestrictSUIDSGID': 'true',
     'PrivateUsers': 'true',