fix: auto-create .claude/current-mode if missing for coordination hooks

The UserPromptSubmit hook requires .claude/current-mode to determine work mode
and gate coordination lock checks. This file is machine-local (gitignored) but
had no initialization logic for fresh clones, causing hooks to fail.

Changes:
- check-messages.sh: Added auto-creation logic with "general" as default
- CLAUDE.md: Documented auto-initialization behavior
- ONBOARDING.md: Added machine-local configuration section
- session-logs/2026-05-19-session.md: Documented investigation and fix

Impact:
- Fixes coordination hooks on all machines
- Prevents first-clone hook failures
- No manual setup required
- Backwards compatible

Resolves: "cood hook seems to be broken on all my machines"

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.claude/scripts/check-messages.sh

@@ -5,6 +5,14 @@ API="http://172.16.3.30:8001"
 SCRIPT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
 MODE_FILE="${SCRIPT_DIR}/current-mode"
 
+# --- Initialize mode file if missing -----------------------------------------
+# The mode file is machine-local (gitignored) and required by this hook.
+# If missing, create it with "general" as the default mode.
+if [ ! -f "$MODE_FILE" ]; then
+  echo "general" > "$MODE_FILE"
+  echo "[INFO] Created .claude/current-mode with default mode: general" >&2
+fi
+
 # Read short username alias from identity.json (if present)
 IDENTITY_FILE="${SCRIPT_DIR}/identity.json"
 USER_ALIAS=""