Add ward init subcommand

[jstockdi]

Summary

• Add ward init subcommand that auto-configures Claude Code hooks in ~/.claude/settings.json
• Supports --dry-run (preview), --force (overwrite), and --remove (clean up) flags
• Preserves existing non-ward hooks and other settings keys during merge and removal

Implementation

• New src/init.rs module with hook configuration builder, JSON merge logic, and ward hook detection
• Init variant added to Command enum in src/cli.rs with three boolean flags
• src/main.rs restructured to handle init before stdin parsing (init does not read stdin)
• 10 unit tests in init.rs covering merge, strip, and detection logic
• 12 integration tests in tests/test_init.rs covering all subcommand modes and edge cases

Test plan

• ward init creates settings.json from scratch with all five hook events
• ward init --dry-run prints config to stdout without writing files
• ward init errors when ward hooks already exist, suggesting --force
• ward init --force replaces existing ward hooks while preserving non-ward hooks
• ward init --remove strips ward hooks and cleans up empty events/hooks keys
• Non-ward hooks and other settings keys are preserved in all operations
• ward init does not block on stdin
• All 139 existing + new tests pass with no warnings

Closes #1