Add SPI badges, fix docs URL, and harden test helper with timeout

[couchdeveloper]

Changes

README

• Add Swift Package Index badges for supported Swift versions and platforms

Documentation

• Fix package URL in SwiftUIFirst.md: your-org → couchdeveloper

Tests

• Convert embedInWindowAndMakeKey to a throwing function with a configurable timeout parameter (default 1 s); times out with EmbedInWindowAndMakeKeyTimeoutError if onAppear never fires
• Remove the redundant readyExpectation pattern across tests — readiness is now guaranteed by the helper itself
• Extract 5_000_000_000 ns timeout into local let timeout constants for clarity
• Add #expect(capturedInput != nil) assertion after embed in the ticker test

Notes

Squash-merge target: main