[Homebrew] Replace the placeholder man command with a real viewer

[brandonpayton]

Why

The shell currently gets a placeholder man command from posix-utils-lite.
That command only copies a raw file from one hard-coded directory. It does not
provide normal section lookup, roff formatting, compressed pages, manual-page
search, or terminal paging.

This change uses mandoc, a small ISC-licensed manual-page toolset, to provide the
normal man experience through Kandelo's Homebrew package path.

What changes

• Add upstream mandoc 1.14.6 from its official archive and verified checksum.
• Cross-build it with an explicit Kandelo feature table. Upstream's configure
  script runs compiled probes, so using host probe results would describe the
  build machine instead of the WebAssembly target.
• Use the tap's normal zlib dependency for compressed pages and less
  dependency for interactive paging.
• Instrument man for its real fork/exec pager path.
• Use Homebrew's normal global share/man links. The page itself remains in
  the package's versioned Cellar directory, so opening one page can materialize
  only the bottle that owns it.
• Keep direct filename lookup as the normal viewing path. Automatically building
  one global mandoc.db would scan every deferred package and defeat lazy
  bottle retrieval. Users can still run makewhatis, and whatis/apropos
  work against the resulting database.
• Remove the placeholder man link from posix-utils-lite and bump that
  Formula to revision 1 so an old bottle cannot silently keep providing it.

The paired Kandelo change in
Automattic/kandelo#1077
removes the placeholder package/rootfs entry and verifies the exact lazy VFS
behavior: global manual-page links remain metadata-only, the first page read
fetches its owning bottle, and unrelated bottles remain deferred.

Runtime coverage

The Formula covers:

• default and explicit manual sections;
• man -w path lookup;
• .so aliases;
• gzip-compressed pages;
• both man and mdoc source formats;
• demandoc and soelim;
• truthful failure for a missing page;
• Homebrew's exact global-symlink-to-Cellar layout;
• makewhatis, whatis, and apropos;
• Chromium formatting; and
• a real PTY pager session through less.

Validation

Exact head: 694ab114827e895ee87af842be20c62f5eee692a

• mandoc source cross-build against ABI 41: passed
• Wasm ABI and required-fork artifact guards: passed
• Node.js runtime checks for the complete command surface above: passed
• Chromium formatting on the same binary build path: passed
• real PTY less fork/exec and quit flow on the same binary build path: passed
• Formula support suite: 94 runs / 853 assertions, no failures
• brew style Formula/mandoc.rb: passed
• Ruby syntax and git diff --check: passed

Rollout

This remains a draft. No bottle publication workflow has been dispatched.

Before publication, the posix-utils-lite source pin must be updated to the
final Kandelo commit that removes the placeholder. The coordinated rollout is:

1. finish the current Dinit rollout;
2. land the paired Kandelo change and pin its immutable source revision here;
3. publish the revised posix-utils-lite bottle;
4. publish the mandoc bottle; and
5. select mandoc in the lazy shell closure.