fix: enhance local snapshot warning and improve disk space calculation for macOS

AGENT.md

@@ -13,8 +13,11 @@ Use this file as the single source of truth for how to work on Mole.
 - Comments must be English, concise, and intent-focused.
   - Use comments for safety boundaries, non-obvious logic, or flow context.
   - Entry scripts start with ~3 short lines describing purpose/behavior.
+- Shell code must use shell-only helpers (no Python).
+- Go code must use Go-only helpers (no Python).
 - Do not remove installer flags `--prefix`/`--config` (update flow depends on them).
 - Do not commit or submit code changes unless explicitly requested.
+- You may use `gh` to access GitHub information when needed.
 
 ## Architecture
 

lib/clean/system.sh

@@ -280,7 +280,8 @@ clean_local_snapshots() {
 
     if [[ "$DRY_RUN" != "true" ]]; then
         if [[ ! -t 0 ]]; then
-            echo -e "  ${YELLOW}!${NC} Local snapshots found, skipping non-interactive mode"
+            echo -e "  ${YELLOW}!${NC} ${#snapshots[@]} local snapshot(s) found, skipping non-interactive mode"
+            echo -e "  ${YELLOW}${ICON_WARNING}${NC} ${GRAY}Tip: Snapshots may cause Disk Utility to show different 'Available' values${NC}"
             return 0
         fi
         echo -e "  ${YELLOW}!${NC} Time Machine local snapshots found"

lib/core/base.sh

@@ -171,7 +171,12 @@ detect_architecture() {
 # Get free disk space on root volume
 # Returns: human-readable string (e.g., "100G")
 get_free_space() {
-    command df -h / | awk 'NR==2 {print $4}'
+    local target="/"
+    if [[ -d "/System/Volumes/Data" ]]; then
+        target="/System/Volumes/Data"
+    fi
+
+    df -h "$target" | awk 'NR==2 {print $4}'
 }
 
 # Get Darwin kernel major version (e.g., 24 for 24.2.0)