chore: add lint workflow and fix lint findings

[udondan]

Adds .github/workflows/lint.yml, which lints every file type in the repo with one blocking job per linter, and fixes every existing finding so the jobs are green from the start.

Job	Tool	Config
swift	SwiftLint 0.65.1 (--strict)	.swiftlint.yml
markdown	markdownlint-cli2 (action v24.2.0)	.markdownlint-cli2.yaml
markdown-links	lychee v0.24.2 (action v2.9.0)	lychee.toml
makefile	checkmake v0.3.2	defaults
yaml	yamllint 1.38.0 (--strict)	.yamllint.yml
actions	actionlint 1.7.12 (plus shellcheck on run: blocks)	defaults
shell	shellcheck	defaults
json	jq empty (syntax only)	–

Third-party actions are SHA-pinned. Downloaded binaries are pinned by version and checked against the SHA-256 digest of the release asset. CHANGELOG.md is excluded because release-please generates it.

Fixes

• Swift:
  • SwiftLint autocorrections: trailing commas, redundant = nil, whitespace.
  • Wrapped long lines. Help strings are joined with + inside ArgumentHelp(...), so the --help text is unchanged.
  • Switch cases dedented to Swift style.
  • Store → eventStore, repeat_ → repeatFrequency.
  • The weekday tuple is now a WeekdayName struct.
  • Rules are disabled only where they conflict with a deliberate pattern, with the reason in .swiftlint.yml: file_length/type_body_length for the by-design large files, function_parameter_count for the testable free functions, and todo.
  • A few single exceptions are marked with swiftlint:disable:next and a comment explaining why.
• Makefile: added the all and test phony targets.
• Shell: one SC2016 exception for literal backticks in check-skill-json-fields.sh.
• Markdown: a descriptive link text in the README instead of "here".
• CLAUDE.md: documents the lint workflow and the lint commands.

Verification

• Every linter exits 0 locally.
• swift build -Xswiftc -warnings-as-errors and swift test -Xswiftc -warnings-as-errors pass (434 tests).
• --help output of the root command and every subcommand is byte-for-byte identical to main.
• check-skill-json-fields.sh passes.