Add timeout command support for macOS (#108)

* feat(timeout): add cross-platform timeout support for macOS

Add portable timeout wrapper that automatically detects and uses the
appropriate timeout command based on the platform:
- Linux: Uses standard GNU `timeout` from coreutils
- macOS: Uses `gtimeout` from Homebrew coreutils

Changes:
- Add lib/timeout_utils.sh with detect_timeout_command() and
  portable_timeout() functions
- Update ralph_loop.sh to source timeout_utils.sh and use
  portable_timeout for Claude Code execution
- Update install.sh to check for coreutils on macOS and provide
  installation instructions
- Update test mocks to include gtimeout and portable_timeout
- Update README.md with macOS coreutils installation instructions
- Update CLAUDE.md with timeout_utils.sh documentation

Users on macOS now need to install coreutils: brew install coreutils

* Update model reference in opencode-review workflow

* Update model name in opencode-review workflow

* Update model version in opencode-review workflow

* Update model version in opencode-review workflow

* Update lib/timeout_utils.sh

Co-authored-by: macroscopeapp[bot] <170038800+macroscopeapp[bot]@users.noreply.github.com>

* Update opencode-review.yml

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: macroscopeapp[bot] <170038800+macroscopeapp[bot]@users.noreply.github.com>

ralph_loop.sh

@@ -8,6 +8,7 @@ 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/timeout_utils.sh"
 source "$SCRIPT_DIR/lib/response_analyzer.sh"
 source "$SCRIPT_DIR/lib/circuit_breaker.sh"
 
@@ -866,7 +867,7 @@ execute_claude_code() {
     if [[ "$use_modern_cli" == "true" ]]; then
         # Modern execution with command array (shell-injection safe)
         # Execute array directly without bash -c to prevent shell metacharacter interpretation
-        if timeout ${timeout_seconds}s "${CLAUDE_CMD_ARGS[@]}" > "$output_file" 2>&1 &
+        if portable_timeout ${timeout_seconds}s "${CLAUDE_CMD_ARGS[@]}" > "$output_file" 2>&1 &
         then
             :  # Continue to wait loop
         else
@@ -879,7 +880,7 @@ execute_claude_code() {
 
     # Fall back to legacy stdin piping if modern mode failed or not enabled
     if [[ "$use_modern_cli" == "false" ]]; then
-        if timeout ${timeout_seconds}s $CLAUDE_CODE_CMD < "$PROMPT_FILE" > "$output_file" 2>&1 &
+        if portable_timeout ${timeout_seconds}s $CLAUDE_CODE_CMD < "$PROMPT_FILE" > "$output_file" 2>&1 &
         then
             :  # Continue to wait loop
         else