Add buf source edit command with --deprecate flag

Adds a new `buf source edit` command that edits Protobuf source files
in-place. The command supports a `--deprecate` flag that adds
`option deprecated = true;` to types matching a FQN prefix.

Key features:
- Component-based FQN matching (foo.bar matches foo.bar.baz)
- Recursive deprecation for packages, messages, enums, services, RPCs
- Multiple --deprecate flags supported
- -d/--diff flag to preview changes without modifying files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>