Roll out ecosystem code-style policy (full sweep)

[gsdali]

What

Roll out the ecosystem's proposed code-style policy to this repo, following the reference
implementation already trialled in OCCTSwiftScripts
(#114 /
#115): a full sweep, not a
gradual exemption-manifest rollout, chosen because this codebase is small enough to fully
comply in one PR and go straight to a blocking gate.

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

This repo's facts

• ~1,125 Swift lines across 6 files (Sources/SwiftDXF, Sources/dxfdump,
  Tests/SwiftDXFTests). Very small: full sweep, trivially so. No exemption manifest needed.
• Zero first-party C++ bridge files. No clang-format needed.
• Already has 6 mandatory OKF policies onboarded (okf/policies/). This adds a 7th.
• No existing .github/workflows/ CI today. This bootstraps CI from nothing.

Scope for this repo

• .swift-format (100 col, 4-space, copied verbatim from OCCTSwiftScripts) + a full
  swift-format --in-place sweep of Sources/ and Tests/.
• .swiftlint.yml, scoped to only_rules: [orphaned_doc_comment] (same pattern as
  OCCTSwiftScripts, to avoid fighting swift-format's own formatting opinions).
• Scripts/comment-ratio-check.sh: report-only nudge (never fails), bash to match this
  repo's own tooling convention (tools/oracle.py aside, no existing Scripts/ dir yet).
• .github/workflows/code-style.yml: swift-format lint --strict and
  swiftlint lint --strict as blocking gates, comment-ratio as a non-blocking step.
• okf/policies/code-style.md, linked from okf/index.md, this repo's 7th mandatory
  policy.
• Hand-fix every remaining swift-format lint --strict / swiftlint lint --strict
  finding after the automatic sweep, the same way OCCTSwiftScripts#115 did.

Explicitly out of scope here

• clang-format — no first-party C++ in this repo.
• The Swift-symbol docs-drift checks proposed for OCCTSwift in the wider proposal (§3b) —
  not part of this pilot-pattern rollout, same as OCCTSwiftScripts#114's own scoping.

Process

Filed per the ecosystem policy's own gate: no repo implements without a filed issue first.
PR to follow, referencing this issue. Holding for review before merge.