Fix install script to install all man pages

install.sh now installs every man page from the release tarball,
routing each to the correct section directory by file extension.
Renamed MAN_DIR to MAN_BASE since it now points at the man base
directory, not a specific section subdirectory.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Sync documentation across all surfaces

Fix stale references in CLAUDE.md and SKILL.md to reflect convert
command and section-aware prompting. Broaden SKILL.md description
and intro beyond "CLI tools." Add convert section to README with
usage examples and ronn credit. Remove hardcoded version from
SKILL.md frontmatter (git tag is the source of truth). Link LICENSE
from README.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add convert command, section-aware prompting, ronn-format docs

Add mansplain convert: goldmark-based ronn-format markdown to mdoc
compiler. No LLM required. Supports title lines, definition lists,
code blocks, cross-references, and inline markup.

Add section-aware prompting: SKILL.md now has guidance for sections
1, 5, and 7. User prompt includes section description. Lint relaxes
SYNOPSIS requirement for section 7 pages.

Broaden SKILL.md triggers beyond CLI tools to cover config files,
overviews, and general project documentation. Instruct agents to
use full project knowledge, not just README and --help.

Include ronn-format(7) man page from upstream ronn repo. Update
man page, README, and help text with section 5/7 examples, convert
documentation, and ronn acknowledgment.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Tidy go.mod: promote direct dependencies

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>