test: add SPM test harness covering Hotkey, ConfigFile, NudgeKind, EventStore

[StuBehan]

Summary

Adds a swift test suite covering the panel's pure-logic surfaces. Shipping binaries are still built by swiftc directly via build.sh — Package.swift exists only so the test runner has somewhere to live.

Test coverage

• HotkeyTests — parse/encode for all modifier aliases (cmd / command, opt / alt / option, ctrl / control), named keys (space / return / tab / escape), digits, multi-modifier combos. Empty / unknown-key error paths. Round-trip encode(parse(spec)) preserves canonical form.
• ConfigFileTests — comments, blank lines, quoted values, prefix-collision guards (STACKNUDGE_VOICE_NAME vs STACKNUDGE_VOICE), in-place replacement vs append, comment-line preservation, bool() truthy/falsy/default handling, case-insensitivity.
• NudgeKindTests — wire-format mapping (stop / permission / unknown → other), case-sensitivity expectations.
• EventStoreTests — append truncation at maxEvents, selection on append/remove, selectNext / selectPrevious clamping, empty-store no-op, selectedEvent derivation.

39 test cases total.

Refactor (small, surface-preserving)

ConfigFile now exposes pure parse(_:) and apply(_:key:value:) helpers; read() / write(_:_:) are thin disk wrappers. No call-site changes — every caller still uses read() / write() / bool() / path.

Build / CI

• Package.swift declares one library target pointing at panel/ + shared/ in place — no source-tree restructuring. The build.sh swiftc path keeps working in parallel.
• .github/workflows/ci.yml gains a test-macos job that runs swift test on macos-15 (Xcode preinstalled).
• Makefile gets make test; prints a friendly Xcode-required message when XCTest isn't reachable (Command Line Tools-only installs).
• .gitignore covers .build/ and Package.resolved.
• CONTRIBUTING.md documents the local Xcode requirement.

Misc

Default voice changed from af_heart to af_aoede across Speaker.swift, PanelNav.swift, notify.sh, notify.conf.example.

Test plan

• swift build (Package.swift) succeeds
• make build (swiftc path) still produces a working arm64 binary
• shellcheck -S warning and bash -n clean on every tracked .sh
• plutil -lint clean on both Info.plists
• swift test runs green in CI (the new test-macos job)

🤖 Generated with Claude Code