chore(#53): roll out the ecosystem code-style policy

[gsdali]

What & why

Rolls out the ecosystem's code-style policy
(ecosystem docs/code-style-policy-proposal-2026-08.md),
following OCCTSwiftScripts#114 /
#115 as the reference
implementation for a repo this size: full sweep, not a gradual exemption manifest. This repo is
small (~2,280 Swift lines across ~19 files, all pure Swift, zero first-party C++ bridge files
despite "bridge" being in the repo's own description), small enough to sweep into full compliance
in one PR and go straight to a blocking gate.

Adds:

• .swift-format (100 col, 4-space, the ecosystem's one deliberate divergence from Google's
  2-space default), copied verbatim from OCCTSwiftScripts, plus a full swift-format --in-place
  sweep of Sources/+Tests/.
• .swiftlint.yml, deliberately narrow (only_rules: [orphaned_doc_comment]), also copied from
  OCCTSwiftScripts' pattern. SwiftLint's default rule set duplicates swift-format's formatting
  opinions (can disagree with them on the same line) and separately opens a large
  code-quality/complexity surface (identifier_name, cyclomatic_complexity,
  function_body_length, nesting, ...) that overlaps the ecosystem's own code-structure
  policy rather than this one; identifier_name's default alone produced 149 hits measured fresh
  for this repo (not carried over from OCCTSwiftScripts' own number), all short conventional
  locals (i, p, n, db) in dense numerical/graph code, none real problems. Scoped down to
  the one rule that catches something swift-format has no equivalent for.
• Scripts/comment-ratio-check.sh: report-only nudge (never fails), matching OCCTSwiftScripts'
  own bash-script convention. This repo had no Scripts/ directory before; this bootstraps one.
• .github/workflows/code-style.yml: swift-format lint --strict and swiftlint lint --strict
  as blocking gates, comment-ratio as a non-blocking step. Pure text analysis, no swift build
  needed. This repo had no CI before; this bootstraps CI from nothing.
• okf/policies/code-style.md: this repo's 7th mandatory policy, linked from okf/index.md
  (this repo's bundle: context-first, docs-current, writing-style, search-before-building,
  code-structure, issue-tracking, and now code-style).
• Hand-fixes for the lint-only findings neither tool auto-fixes, the same categories
  OCCTSwiftScripts#115 hit:
  • BeginDocumentationCommentWithOneLineSummary: a blank /// line added after the
    one-sentence summary in ~14 doc comments across CADFileLoader.swift,
    FaceIdentityTable.swift, EdgeIdentityTable.swift, VertexIdentityTable.swift, and one
    test file.
  • ValidateDocumentationComments: Returns: sections added to PointConverter.pointsToBody,
    BodyUtilities.makeMarkerSphere, SurfaceConverter.surfaceToGridBodies,
    WireConverter.wireToBody, and CADFileLoader.shapeToBodyAndMetadata; a Throws: section
    added to CADFileLoader.load; four singular - Parameter x: blocks converted to plural
    - Parameters: blocks (CADFileLoader.load, CADFileLoader.shapeToBodyAndMetadata,
    WireConverter.wireToBody), which surfaced that the plural form is validated for
    completeness against the full parameter list, by internal name where it differs from the
    external label (bodyID/rgba/customDeflection/useDirectMesh, not
    id/color/deflection/directMesh), not just the params that already had prose.
  • No AlwaysUseLowerCamelCase or EndOfLineComment findings this pass, and no
    orphaned_doc_comment findings from SwiftLint either.
• Incidental: cleared every em-dash found in every file touched by this sweep (source, tests, the
  new scaffold files, and the one pre-existing em-dash in okf/index.md's frontmatter
  description), per the ecosystem's writing-style policy's own "clear them from any file you are
  already editing" instruction.

Explicitly out of scope here (see the issue): clang-format (no first-party C++ in this
repo), and the Swift-symbol docs-drift checks proposed for OCCTSwift, tracked separately if this
repo's docs/reference/ (which documents Swift declarations directly, unlike OCCTSwiftScripts'
CLI-verb docs) turns out to need them.

Zero behavior change. Every change is a doc comment, a formatting pass, or CI/policy
scaffolding; no function signature or logic changed. Verified directly, not just asserted:

• swift-format lint --strict and swiftlint lint --strict both report zero violations
  (find Sources Tests -name '*.swift' -print0 | xargs -0 swift-format lint --strict --configuration .swift-format; swiftlint lint --strict --config .swiftlint.yml).
• swift build and swift test run before and after the sweep give identical results: build
  succeeds both times, and both times swift test reports 45 tests in 9 suites, all passing.
• No Package.resolved drift from any local build/test run.

Closes #53

Checklist

• New or changed behavior is covered by a unit test in the same PR (not just manual
  verification); see SecondMouseAU/OCCTReconstruct#397
  for the ecosystem-wide test-coverage standard this is piloting.
  N/A here: no behavior changed (formatting/doc comments/CI/policy only), verified via the
  existing test suite (45/45 passing, identical before and after) rather than new tests,
  since there is no new behavior for a new test to cover.

Notes for the reviewer

Per the ecosystem's own gate (no repo implements without a filed issue first), this was filed as
#53 before any of this landed. Holding for review before merge, not merging this myself.