test: every linked config must belong to a tool

[YASoftwareDev]

What

Every config directory the install links must declare how its tool is obtained:

policy	meaning
installer	the repo provides the tool (function named and verified to exist)
guarded	the linking path tests has <tool> first
prerequisite	declared here WITH a reason

An undeclared config dir fails, so nobody can add config for an uninstalled tool
without saying so.

Why

The no-sudo tmux bug was never "tmux was missing". It was the repo linking tmux
config and cloning tmux plugins for a tmux that was not there, so a host looked
configured while nothing could use it. 1.13.2 fixed that instance by hand. Nothing
stopped the next one - and tests/no-fixture-masking.py cannot see this class at
all, which it states in its own output. This is the other half.

Current state, all six linked dirs declared and verified:

git       tool=git    policy=prerequisite
nvim      tool=nvim   policy=installer
ripgrep   tool=rg     policy=installer
tmux      tool=tmux   policy=guarded
yazi      tool=yazi   policy=installer
zsh       tool=zsh    policy=guarded

Why a table and not inference

Two things are not inferable, and pretending otherwise is how a checker becomes a
placebo:

• A dir name does not name its tool - ripgrep/ configures rg.
• "Is this a fair prerequisite?" is judgment. git is one because you cannot
  obtain this repo without it; the script must not decide that itself.

The table also names the function to verify. Inferring it was wrong three ways
on the first run - install_neovim not _install_nvim, _install_ripgrep not
_install_rg, and zsh's guard lives in install_zsh while the symlink is one call
away in _link_zshrc. That produced three false findings against entirely correct
code. Declaring the name is honest; guessing was not.

Red-proof

Each mutation rc=1, control rc=0:

mutation	finding
remove the 1.13.2 tmux guard	'tmux' claims policy 'guarded': install_tmux() does not test \has tmux``
add an undeclared config dir	config dir 'newtool' is linked but not declared in POLICY
rename a declared installer	'ripgrep' claims policy 'installer' via _install_ripgrep(), which does not exist

Limit, printed in its own verdict

guarded is recognised by a has <tool> test inside the named function or one call
away. A guard written another way reads as absent, and deeper call chains are not
followed. Stated rather than silently approximated.

Verified

test.sh workstation 62/63, 0 failures; lint-workflows PASSED;
ci-gate-covers-all passes (no new job); no-fixture-masking PASSED.