fix(plugin-dev): validate-hook-schema.sh handles plugin hooks.json format

[sorapallivenkatesh]

Problem

The hook-schema validator shipped in the plugin-dev plugin's Hook Development skill (plugins/plugin-dev/skills/hook-development/scripts/validate-hook-schema.sh) has two bugs that make it fail on valid configurations — including the exact format the skill itself documents.

1. Crashes on plugin hooks.json files.
The validator only understood the flat settings format, where hook events live at the top level. But plugin hooks.json uses a wrapper — events nested under a "hooks" key alongside an optional "description" — which is the format documented in SKILL.md and used by every bundled plugin (hookify, security-guidance, ralph-wiggum, …). Given a real plugin hooks.json, the validator treated description and hooks as event names and then crashed:

⚠️  Unknown event type: description
⚠️  Unknown event type: hooks
jq: error (at hooks.json:49): Cannot index string with number

2. Treats matcher as required.
It reported ❌ Missing 'matcher' field for any hook entry without a matcher. But matcher is optional: it only applies to PreToolUse/PostToolUse (to target specific tools), and even there an absent matcher means "match all". Events like Stop, SessionStart, and UserPromptSubmit never carry one, so valid configs failed validation.

Fix

• Detect the config format and unwrap the plugin {"hooks": {...}} wrapper (ignoring description); fall back to the flat settings format.
• Stop treating matcher as required.

No behavior change for genuinely invalid configs — missing hooks arrays, bad hook type, missing command/prompt, and non-numeric timeouts are still reported.

Verification

Input	Before	After
plugins/hookify/hooks/hooks.json (wrapper)	crash	✅ passes
plugins/security-guidance/hooks/hooks.json (wrapper, matchers, timeouts)	crash	✅ passes
flat settings config with a matcher-less Stop hook	❌ false "Missing matcher"	✅ passes
deliberately broken config (missing hooks array, bad type, missing command, bad timeout)	errors	✅ still errors (exit 1)