Roll out code-style policy CI: swift-format + SwiftLint + comment-ratio check

[gsdali]

What

Roll out the ecosystem's proposed code-style policy here, following OCCTSwiftScripts as the
reference implementation for a repo this size (small: full sweep, not a gradual manifest).

Proposal doc: ecosystem docs/code-style-policy-proposal-2026-08.md

Precedent: OCCTSwiftScripts#114
(tracking issue) and OCCTSwiftScripts#115
(the PR that did the sweep); this repo repeats that pattern exactly.

Why full sweep, not a manifest

This repo is small: ~2,280 Swift lines across ~19 files (Sources/OCCTSwiftTools +
Tests/OCCTSwiftToolsTests), all pure Swift, zero first-party C++ bridge files. Small enough to
sweep into full compliance in one PR and go straight to a blocking gate, the same reasoning
OCCTSwiftScripts#114 used, rather than needing OCCTSwift's gradual "if you touch it, you fix it"
exemption-manifest approach.

Scope for this repo

• .swift-format (100 col, 4-space) + .swiftlint.yml (scoped to avoid fighting swift-format:
  orphaned_doc_comment on, formatting-overlap rules off): copied verbatim from
  OCCTSwiftScripts.
• A comment:code ratio check, Scripts/comment-ratio-check.sh (bash, report-only, never fails),
  matching OCCTSwiftScripts' own convention. This repo has no Scripts/ directory today, so this
  bootstraps one.
• A full sweep of Sources/ + Tests/ into compliance in the same PR (swift-format --in-place --recursive, plus hand-fixes for lint-only findings neither tool auto-fixes).
• A new blocking CI job, .github/workflows/code-style.yml, wiring swift-format lint --strict
  and swiftlint lint --strict as blocking gates and the comment-ratio check as non-blocking.
  This repo has no CI today, so this bootstraps CI from nothing.
• okf/policies/code-style.md, linked from okf/index.md, bumping the mandatory-policy count
  from six to seven (this repo's OKF bundle currently lists: context-first, docs-current,
  writing-style, search-before-building, code-structure, issue-tracking).

Explicitly out of scope here

• clang-format: no first-party C++ bridge files in this repo (confirmed: zero .cpp/.mm/
  .h/.hpp under Sources/Tests), despite "bridge" being in the repo's own description
  (bridge layer between the OCCTSwift kernel and the OCCTSwiftViewport renderer); it is a pure
  Swift bridge, no C++ involved.
• The Swift-symbol docs-drift checks (check-docs-completeness.py etc.) proposed for OCCTSwift
  in the wider proposal: out of scope for this pass, same as OCCTSwiftScripts#114.

Process

Filed per the ecosystem policy's own gate: no repo implements without a filed issue first. PR to
follow, referencing this issue. Zero behavior change intended: formatting/doc-comment/CI only.
Hold for review before merge.