fix: address Codex review — sanitize search, privacy gate, ETHOS.md sidecar

Three fixes from adversarial Codex review:
- /investigate: sanitize error messages before searching (strip hostnames,
  IPs, file paths, SQL, customer data). Skip search if unsanitizable.
- /office-hours: add privacy gate before landscape search. Use generalized
  category terms, never the user's specific product name or stealth idea.
- setup: link ETHOS.md into .agents/skills/gstack/ sidecar so workspace-
  local Codex sessions can find the builder philosophy.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

setup

@@ -205,6 +205,17 @@ create_agents_sidecar() {
       fi
     fi
   done
+
+  # Sidecar files that skills reference at runtime
+  for file in ETHOS.md; do
+    local src="$GSTACK_DIR/$file"
+    local dst="$agents_gstack/$file"
+    if [ -f "$src" ]; then
+      if [ -L "$dst" ] || [ ! -e "$dst" ]; then
+        ln -snf "$src" "$dst"
+      fi
+    fi
+  done
 }
 
 # 4. Install for Claude (default)