Add a touchscreen right click and a seam for the release-bypass tests

[thirteen37]

Closes the two loose ends left after #40.

Two-finger tap → right click

Restricting the secondary tap recognizer to .indirectPointer in #40 fixed taps arriving as right clicks, but left no way to right-click at all without a trackpad or mouse attached. A two-finger tap now fills that gap, routed through the existing emitClick(buttonNumber: 1, …) so it inherits the same 50 ms hold.

It's restricted to .direct touches deliberately: a trackpad's two-finger tap already arrives as an indirect secondary click, so without the restriction both recognizers would fire for one gesture.

Checked for conflicts — a stationary two-finger tap starts neither the pan (needs movement past slop) nor the pinch (needs a scale change), so wheel scrolling and zoom are unaffected.

Long-press was the alternative convention. It collides with the one-finger drag, which handlePan already treats as a held left button, so pausing before a drag would fire a spurious right click first.

ViewerViewModel test seam

sendInputRelease bypasses the capture guard on purpose — a button or key held when capture is switched off would otherwise stay pressed on the host forever. That was only verified by reading it, because the session was built internally with no way to substitute one.

init now takes a defaulted session: parameter, so every existing call site is unchanged, and MockKVMSession records what reaches the session.

Verification

Both new behaviours were checked against a deliberately broken version, not just a green run. Adding guard isMouseCaptureEnabled back onto the bypass fails the test with:

XCTAssertEqual failed: ("0") is not equal to ("1")

Test plan

• KVMCore 171/171 (+4 view-model tests)
• iPadOS 20/20 (+1 two-finger tap test)
• macOS suite passes
• Release-bypass test verified to fail when the bypass is guarded
• Hardware: two-finger tap produces a right click on the host
• Hardware: one-finger tap still produces a left click, and two-finger scroll still scrolls
• Hardware: trackpad right click produces exactly one right click, not two

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