Add Strata native macOS hex editor

[ConnorHowell]

Summary

• Complete native macOS hex editor built in Swift/AppKit targeting macOS 13+, visually inspired by HxD
• NIB-free programmatic UI with piece table edit engine, viewport-culled Core Graphics rendering, and memory-mapped I/O for large file support
• Multi-tab sessions, Data Inspector sidebar with LE/BE and decimal/hex toggle, HxD-style tabbed Find/Replace dialog (text/hex/integer/float search)
• Includes Myers diff engine, checksum panel (CRC-16/32, MD5, SHA-1, SHA-256), Intel HEX and S-Record import/export, drag-and-drop file support
• 77 unit tests covering PieceTable, DiffEngine, ChecksumEngine, IntelHex, and SRecord plus 7 UI tests

Test plan

• make build compiles without errors
• make test passes all 77 unit tests and 7 UI tests
• make lint passes SwiftLint checks
• Open a binary file and verify hex grid rendering with alternating byte colors
• Test mouse click and drag selection across hex and ASCII panes
• Verify Data Inspector updates on cursor movement with LE/BE and decimal/hex toggles
• Test Find dialog (Cmd+F) across all four tabs: text, hex, integer, float
• Test Go To Offset (Cmd+G) navigation
• Verify drag-and-drop file opening onto window and dock icon

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