chore: add crates.io metadata to Cargo.toml

Add repository, homepage, documentation, keywords, categories,
and readme fields for crates.io publishing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: copyleftdev

Cargo.toml

@@ -4,6 +4,12 @@ version = "0.1.0"
 edition = "2021"
 description = "Single-binary webhook inbox. Accept HTTP, store it, show it."
 license = "MIT"
+repository = "https://github.com/copyleftdev/hookbin.dev"
+homepage = "https://hook-bin.dev"
+documentation = "https://github.com/copyleftdev/hookbin.dev#readme"
+keywords = ["webhook", "http", "inspector", "debugging", "sqlite"]
+categories = ["command-line-utilities", "development-tools", "web-programming::http-server"]
+readme = "README.md"
 
 [[bin]]
 name = "hookbin"