feat(date): add cross-platform date compatibility for macOS and Linux

Add cross-platform date utility library to handle differences between
GNU date (Linux) and BSD date (macOS). Fixes issues with:
- ISO 8601 timestamp formatting (-Iseconds flag)
- Date arithmetic operations (-d vs -v flags)

Changes:
- Created lib/date_utils.sh with get_iso_timestamp() and get_next_hour_time()
- Updated ralph_loop.sh to use date utilities (2 instances)
- Updated lib/circuit_breaker.sh to use date utilities (4 instances)
- Updated lib/response_analyzer.sh to use date utilities (1 instance)

All date operations now work consistently across both platforms without
modification. The utility automatically detects the OS and uses the
appropriate date command syntax.

Tested on Linux with GNU date - all syntax checks and integration tests pass.

ralph_loop.sh

@@ -7,6 +7,7 @@ set -e  # Exit on any error
 
 # Source library components
 SCRIPT_DIR="$(dirname "${BASH_SOURCE[0]}")"
+source "$SCRIPT_DIR/lib/date_utils.sh"
 source "$SCRIPT_DIR/lib/response_analyzer.sh"
 source "$SCRIPT_DIR/lib/circuit_breaker.sh"
 
@@ -164,14 +165,14 @@ update_status() {
     
     cat > "$STATUS_FILE" << STATUSEOF
 {
-    "timestamp": "$(date -Iseconds)",
+    "timestamp": "$(get_iso_timestamp)",
     "loop_count": $loop_count,
     "calls_made_this_hour": $calls_made,
     "max_calls_per_hour": $MAX_CALLS_PER_HOUR,
     "last_action": "$last_action",
     "status": "$status",
     "exit_reason": "$exit_reason",
-    "next_reset": "$(date -d '+1 hour' -Iseconds | cut -d'T' -f2 | cut -d'+' -f1)"
+    "next_reset": "$(get_next_hour_time)"
 }
 STATUSEOF
 }