Whole-tree treefmt drift: ~96 files fail --fail-on-change

Running whole-tree `treefmt --fail-on-change` currently fails on roughly 96 files that drifted from the configured formatters before the current server work began — across docs/, SPEC.md, and the Rust crates. Discovered while verifying the shared test-harness stage of #107, whose own files are format-clean; stage verification is scoped to touched files as a workaround.

Suggested fix: one dedicated formatting sweep commit (no logic changes), after which whole-tree `treefmt --fail-on-change` becomes enforceable again in CI and review. Doing it piecemeal inside feature branches pollutes their diffs.

Run whole-tree `treefmt --fail-on-change` and review the reported files across docs/, SPEC.md, and the Rust crates. Apply only the configured formatting in a dedicated sweep commit, then rerun the same command; done means it passes without logic changes.

Written by the indexing model from the issue text.