fibermargin 0.1.0

• Stabilized the four-argument refine_spatial_labels() public API.
• Added strict validation for coordinate dimensionality, finite values, labels, specimen identifiers, worker budgets, and per-specimen coordinate variation.
• Made coordinate dimensionality specimen-specific. Constant axes are removed independently, while genuinely three-dimensional specimens retain all three coordinates.
• Made specimen isolation explicit in the native engine, including local class encodings and support for completely overlapping coordinate systems.
• Replaced platform-specific specimen forking with one cross-platform C++ thread budget. Results and diagnostics are deterministic across worker counts.
• Added pointwise and per-specimen summary diagnostics, including class-loss reporting without imposing class preservation.
• Added 2D, genuine 3D, multi-specimen, invariance, memory, and parallelism tests and expanded the README, vignette, reference documentation, and manuscript.
• Removed persistent vignette option changes and replaced the internal fixed CRC benchmark seed with the optional user-controlled seed argument.