refactor: consume the flat go and react modules

[retr0h]

Renames go::<name> call sites to go-<name> across the justfile, both
workflows, CLAUDE.md, and the docs site, and imports go/go.just instead of
loading go.mod.just.

Configuring the modules

The shared modules ship defaults — go_coverage_target := "100",
react_dir := ".". osapi differs on both, so it sets
allow-duplicate-variables and reassigns them:

set allow-duplicate-variables

react_dir := "ui"
go_coverage_target := "99.9"

import? '.just/remote/go.just'

The assignment is in scope when just parses the file, so every way of running a
recipe agrees:

just react-fmt-check                          → All matched files use Prettier code style!
just go-unit-cov-check                        → coverage 100.0% meets target 99.9%
just go_coverage_target=95 go-unit-cov-check  → coverage 100.0% meets target 95%
just test                                     → same as the above

Earlier revisions of this PR configured the modules by exporting environment
variables. That only reaches recipes invoked as child processes, so
just react-fmt-check used the module default while just test used osapi's
value — one command with two answers. See
specs#46.

Why 99.9%

osapi has nine uncovered statements, all guards that cannot execute — six
defense-in-depth validation.Struct() calls on bodies whose fields are all
omitempty, an error return commented "not coverable: gopsutil always succeeds
on a running system", and three of the same shape. osapi's own guidance requires
keeping them, so 99.9% is the honest figure rather than a waypoint to 100%.

Declared in .github/codecov.yml as well — change both together.

Also

• .mise.toml declares just, which it never did. Without it mise had nothing
  to resolve and the shell fell through to Homebrew's 1.45.0 while CI installs
  1.58.0, and the two disagree on formatting a boolean setting. Declared as
  latest, matching how the workflow's setup action floats.
• just-lint.yml records the just version, so a change in what the setup action
  installs is visible rather than inferred.

Applies converge-justfile-consumption tasks 1.2 and 2.5, and
standardize-repository-layout task 5.1.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main     #439   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files         484      484           
  Lines       24935    24935           
=======================================
  Hits        24921    24921           
  Misses         14       14           

---

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