feat: Add platform support display and Compatible filter

[arimxyer]

Summary

This PR adds platform/environment support information to Taproom, allowing users to:

• See which platforms (macOS, Linux) and architectures (arm64, x86_64) a package supports in the details panel
• Filter packages by compatibility with their current system using the new "Compatible" filter (m key)

Changes

• Data model: Added Platform struct with OS and Arch fields, plus Platforms and MinMacOSVersion fields to Package
• API parsing: Extended apiFormula to parse bottle.stable.files and apiCask to parse variations and depends_on.macos
• Platform detection: Added CurrentPlatform() helper that uses runtime.GOOS and runtime.GOARCH
• Details panel: Shows "Platforms: macOS (arm64, x86_64), Linux (arm64, x86_64)" when available, including minimum macOS version for casks
• New filter: Press m to show only packages compatible with your current system

How it works

For Formulae

Parses bottle.stable.files keys like arm64_sequoia, x86_64_linux to determine platform support.

For Casks

Parses variations keys for platform support, plus depends_on.macos.>= for minimum macOS version requirements.

Test plan

• go build ./... passes
• go test ./... passes
• go vet ./... passes
• Manual testing: Verify platform info displays in details panel for packages like ripgrep
• Manual testing: Verify m filter shows only packages compatible with current system

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