feat(hooks): Add HookResponse parsing and user confirmation support

[pahud]

Description

Implements decision: ask support for PreToolUse hooks, allowing hooks to prompt users for confirmation before tool execution.

Closes #3596

Changes

• Added HookDecision enum (Allow, Ask, Block) and HookResponse struct for parsing JSON responses from hooks
• Updated HookOutput type to include parsed HookResponse
• Added prompt_hook_confirmation() helper for user y/n prompts
• Updated PreToolUse hook handling to process JSON decision responses
• Added unit tests for JSON parsing
• Updated documentation with examples

How it works

PreToolUse hooks can now output JSON to STDOUT with a decision field:

json
{"decision": "ask", "message": "⚠️ This command uses sudo. Allow execution?"}

Exit Code	STDOUT	Behavior
0	Empty	Allow
0	{"decision": "allow"}	Allow
0	{"decision": "ask", "message": "..."}	Prompt user (y/n)
0	{"decision": "block", "message": "..."}	Block, return message to LLM
2	-	Block (existing behavior)

Example hook

#!/usr/bin/env python3
import json, sys, re

input_data = json.load(sys.stdin)
command = input_data.get("tool_input", {}).get("command", "")

if re.search(r'(^|;|&&|\|\||\|)\s*sudo(\s|$)', command):
    print(json.dumps({
        "decision": "ask",
        "message": f"⚠️ This command uses sudo:\n\n  {command}\n\nAllow execution?"
    }))
sys.exit(0)

Testing

• Added unit tests for HookResponse::from_stdout() parsing
• Manual testing with sample hooks