test: extract pure shortcut matching so it can be table-tested

[arzafran]

First slice of #186. Does not close it.

What this does

AppDelegateShortcutRoutingTests is 4,684 lines and 87 tests, and it's slow and flaky for a reason that turns out to be avoidable: the key-matching logic it exercises was already pure, but it lived as private methods on AppDelegate and read one instance property, so the only way to reach it was to build a real window. CI has been paying for that — the class is isolated, run serially, one test permanently skipped, and a retry absorbed because it's timing-sensitive.

This moves the matching into a free function you can call directly, and table-tests it.

Summary

1. Sources/ShortcutRouting.swift (new) — matchStroke and match, bodies moved verbatim. The one change: the layout character provider is a parameter instead of self.shortcutLayoutCharacterProvider, which is what made them impure.
2. Sources/AppDelegate.swift — the two methods become thin forwarders with identical private signatures. No call site changes. 197 lines out, 30 in.
3. programaTests/ShortcutRoutingTests.swift (new) — 18 table rows plus 2 chord tests. No windows, no RunLoop, no UserDefaults, no KeyboardShortcutSettings.

Matrix covered: plain modifier match/mismatch, Return vs keypad Enter, AZERTY digit-symbol ANSI fallback, digit shortcut rejected on the wrong physical key, shifted-digit symbols, Ctrl+H as an ASCII control char, Cmd+Shift+] fallback on a non-US layout, ISO angle-bracket rejection, Russian resolving via the injected provider and its fallback when translation also fails, three Dvorak physical-key cases, and shift-symbol normalization (?→/, {→[).

The old tests stay

Deliberately. They're the safety net proving this move changed nothing — deleting them in the same PR that moves the code would remove the only evidence the move was safe. Retiring them, and unwinding the split-stateful isolation and retry in scripts/ci-run-unit-tests.sh, is the next slice once these have proven equivalent over some real runs.

One judgment call worth a look

Five helpers were only reachable from the moved code. Three had no other callers and moved wholesale. Two — normalizedShortcutEventCharacter and digitForNumberKeyCode — are also used by numberedShortcutDigit, which stays on AppDelegate. Rather than duplicate them into two sources of truth, they became nonisolated static in place. They touch no instance state, so dropping the @MainActor isolation is safe, but it's the one non-mechanical decision here.

Test plan

• xcodebuild -scheme programa → ** BUILD SUCCEEDED ** (done)
• xcodebuild -scheme programa-unit build-for-testing → ** TEST BUILD SUCCEEDED **, with ShortcutRoutingTests.swift confirmed in the compile log (done — a file missing from the pbxproj Sources phase silently doesn't compile rather than erroring, so this was checked explicitly)
• CI green, including the untouched AppDelegateShortcutRoutingTests — if the move broke anything, that suite is what catches it