Prototype deterministic bundled-font artifact formats

[Happypig375]

Parent: #191

Build the reproducible offline artifact foundation before changing the runtime font backend.

Scope

• add a deterministic repository tool for all three bundled OTF sources
• emit a versioned, little-endian compact binary table container with magic/schema and each source font's SHA-256
• emit a generator-only C# representation prototype from the same logical input
• exclude only tables proven unused by CSharpMath (currently GSUB/GPOS), documenting that decision
• check in reproducible artifacts and a manifest; this issue does not switch production rendering yet

Acceptance criteria

• repeated generation is byte-for-byte identical and a verify command regenerates/compares the checked-in outputs
• schema, endian, truncated payload, tampered content, and source-hash mismatches fail clearly
• tests cover all three faces and deterministic ordering
• record binary versus generated-C# sizes, build/startup implications, and trimming/AOT tradeoffs using the Benchmark math-font startup allocations and retained memory #293 methodology
• artifacts preserve every source table needed by the later renderer-data extraction/runtime migration sub-issues
• no runtime behavior or custom LocalTypefaces behavior changes in this phase