chore(#12): roll out the ecosystem code-style policy

[gsdali]

What & why

Roll out the ecosystem's code-style policy to this repo
(ecosystem docs/code-style-policy-proposal-2026-08.md),
following the reference implementation
(OCCTSwiftScripts#114 /
OCCTSwiftScripts#115). This repo is
tiny (~547 Swift lines across 4 files: Sources/SwiftMeshHeal/MeshHeal.swift,
Sources/SwiftMeshHeal/HoleFill.swift, Tests/SwiftMeshHealTests/MeshHealTests.swift), so this is
a full sweep, not a gradual exemption-manifest rollout, 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 --recursive sweep of Sources/ + Tests/.
• .swiftlint.yml, deliberately narrow (only_rules: [orphaned_doc_comment]). 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. 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), bash to match this repo's own
  script convention (not the Python style OCCTSwift/Scripts/ uses).
• .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
  in the gate itself.
• okf/policies/code-style.md: linked from okf/index.md.
• By-hand fixes for every lint-only finding swift-format --in-place could not auto-fix:
  • BeginDocumentationCommentWithOneLineSummary (15 doc comments across MeshHeal.swift and
    HoleFill.swift): inserted a blank /// line after the one-line summary sentence, moving the
    rest of the existing prose into a second paragraph. No content removed.
  • AlwaysUseLowerCamelCase (3 local renames, all inside HoleFill.swift's liepaFill, all
    call sites updated in the same function): P -> points, INF -> inf, Wt -> weightTable.
    Local-only, no public API surface touched.
  • EndOfLineComment (1 finding, Tests/SwiftMeshHealTests/MeshHealTests.swift): moved a
    trailing comment that exceeded the line length onto its own line above the statement.
  • Em-dashes: every em-dash in the two touched source files was replaced with plain punctuation
    (colon, comma, or a second sentence), per the ecosystem's writing-style policy, since these are
    files this PR edits directly.

Explicitly out of scope (see #12):
clang-format (zero first-party C++ bridge files in this repo, confirmed), and any new docs-drift
tooling beyond what this repo's existing docs-current/context-first policies already cover.

Zero behavior change. Renames are local-only; everything else is formatting/doc-comment
restructuring plus the public access modifier moving from the extension declaration to each
member (swift-format's NoAccessLevelOnExtensionDeclaration rule), which does not change the
public API surface. Verified directly, not just asserted:

• swift build and swift test: identical result before and after this sweep (build succeeds,
  7/7 tests pass).
• swift-format lint --strict and swiftlint lint --strict: both report zero violations.
• Scripts/comment-ratio-check.sh: no files at or above the 1.0x threshold.
• No Package.resolved was created or touched (this package has no external dependencies).

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/docs/CI only), verified via the existing
  MeshHealTests suite (7/7 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
#12 before any of this landed. Holding
for review before merge.

Closes #12

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