Rename the tool and all references from "paver" to "pave":
- Cargo.toml crate name
- .paver.toml config file to .pave.toml (with [pave] section)
- All Rust struct names (PaveConfig, PaveSection, PaveFrontmatter)
- All constants (PAVE_HOOK_MARKER)
- All HTML comment markers (<!-- pave:run -->, <!-- pave:expect -->, etc.)
- All documentation and template files
- All site/website files
- All GitHub workflow files

The PAVED framework name remains unchanged (it's an acronym).

Also fixes 4 pre-existing clippy warnings in src/commands/status.rs.

Closes #86