fix(hook-development): recognize all five hook handler types

[fcarvajalbrown]

Problem

The plugin-dev hook-development skill teaches plugin authors how to write hooks.json, but it only knew two of the five hook handler types Claude Code actually supports. Both the docs and the bundled validator had drifted from the product:

• scripts/validate-hook-schema.sh accepted only command and prompt, and reported http, mcp_tool, and agent hooks as errors — even though all three are valid, documented types. So the tool failed valid configs it was meant to certify.
• SKILL.md's "Hook Types" section documented only 2 of the 5 types (the root cause of the drift).
• The event allowlist in the validator was missing many valid events.

Verified against the official docs (https://code.claude.com/docs/en/hooks): the five handler types are command, prompt, http, mcp_tool, and agent.

Changes

• scripts/validate-hook-schema.sh
  • Accept all five handler types instead of erroring on http/mcp_tool/agent.
  • Add per-type required-field validation matching the documented schemas: http -> url, mcp_tool -> server + tool, agent -> prompt.
  • Expand the event allowlist from 9 to the full documented set (adds FileChanged, PostCompact, PermissionRequest, etc.) so valid events are no longer flagged as unknown.
• SKILL.md — add a five-type overview table plus dedicated subsections for HTTP, MCP-tool, and Agent hooks with required/optional fields and examples.
• scripts/README.md — list all five types instead of command/prompt.

Testing

Ran the validator against fixtures built from the official docs:

Case	Before	After
Valid http/mcp_tool/agent config	rejected (Invalid type 'http', exit 1)	passes, exit 0
http hook missing url	(never reached)	errors
mcp_tool missing tool	(never reached)	errors
Genuinely invalid type (webhook)	errors	errors
Config using FileChanged event	"unknown event" warning	no warning
Original command/prompt config	passes	passes (no regression)