feat(security): receipt admin scripts + user git-ops (zero exceptions)

Wire the remaining shell egress through gstack-egress-lib.sh:

- gstack-gbrain-mcp-verify: both JSON-RPC probe POSTs (initialize +
  tools/list) receipted fail-closed via payload files (hash == wire
  bytes). A refused receipt lands in the NETWORK class — no send.
- gstack-security-dashboard / gstack-community-dashboard: the
  community-pulse GETs receipted fail-open (read-only stats must not
  break over an audit hiccup).
- gstack-gbrain-supabase-provision: api_call receipted fail-closed.
  Each retry attempt hands the helper a fresh copy of the body file
  (the helper consumes its payload). The receipt hashes the request
  body only — the PAT never reaches the ledger or any log. Refusal
  exits 8 without retrying.
- git-class sha256:null receipts, fail-open: gstack-artifacts-init
  (ls-remote, initial push, fetch/pull recovery, retry push),
  gstack-brain-restore (staging clone, existing-repo fetch),
  gstack-session-update (self-update pull).

gstack-team-init needs no wiring: every git clone in it is inside an
echoed instruction string, not an executed command.

The lib now self-locates with shell builtins only (no dirname), so
sourcing works under the whitelist-PATH test harnesses.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit b8c5e2055b21ab72878b3e46f8047782ee65a11c)

bin/gstack-egress-lib.sh

@@ -36,7 +36,12 @@
 # their own EXIT traps and a trap set by a sourced library would clobber
 # the caller's. All temp handling is immediate, per call.
 
-_gstack_egress_lib_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# Self-locate without dirname (builtins only), so the lib works even under
+# a stripped test PATH.
+case "${BASH_SOURCE[0]}" in
+  */*) _gstack_egress_lib_dir="$(cd "${BASH_SOURCE[0]%/*}" && pwd)" ;;
+  *) _gstack_egress_lib_dir="$(pwd)" ;;
+esac
 
 _gstack_egress_home() {
   if [ -n "${GSTACK_HOME:-}" ]; then