Migrate CocoaPods → Swift Package Manager (target: Swift port Phase 1)

[schuyler]

Context

CocoaPods is in maintenance mode, and the current dependency set includes three pods from a patched external spec fork (see the vendoring issue and survey §4.1). The dependency overhaul is what makes SPM possible: the post-overhaul set is SPM-native, the current set mostly isn't.

Dependency	Removed by	SPM story
hoedown (patched)	v3000.1.1 parser swap (#77)	replaced by cmark-gfm (SPM or vendored C target)
PAPreferences	v3000.1.2 (#188)	replaced by in-repo wrapper
LibYAML (patched) + YAML-framework	Swift port Phase 1	Yams (SPM)
handlebars-objc (patched)	Swift port Phase 1 (#201)	drop — see #201 discussion (one template; string composition suffices)
MASPreferences	Swift port Phase 4	native replacement
M13OrderedDictionary	#187	removed
Sparkle (disabled)	#129 re-enable	Sparkle 2 is SPM-native
GBCli, JJPluralForm	evaluate	tiny; vendor or replace

Work (at Swift port Phase 1, alongside the bridging-header setup)

• Move remaining dependencies to SPM packages in the Xcode project
• Replace the CocoaPods build phases (Manifest.lock check, resources script) and the Gemfile/Bundler layer
• Update setup.sh and .github/actions/setup-macdown (Ruby/bundler steps go away)
• Keep vendored C (peg-markdown-highlight until v3001.1.x; cmark-gfm if vendored) as local SPM targets or xcframeworks

Interim policy (now → Phase 1)

No new pods. Every milestone that deletes a pod is measured progress toward this issue.

References

• plans/dependency-overhaul-survey.md §4 (branch claude/dependencies-overhaul-planning-hw3lms)
• plans/dependency-overhaul-decisions.md D-20
• Related to Swift Port: Migrate MacDown 3000 from Objective-C to Swift #201, Dependency Upgrade Roadmap and Strategy #190