feat: add RobertEngine — fabric physics module for garment overlay rendering

[Copilot]

Implements the TRYONYOU V10 fabric physics engine that computes garment overlay render metrics (width, height, alpha, sheen) from biometrically-detected volumetry — no user-supplied weight or size required.

New: api/robert_engine.py

• PILOT_FABRIC_PHYSICS — 5 Lafayette collection fabrics with physical properties (drape coefficient, GSM, elasticity, friction)
• calculate_lafayette_factor — silhouette width multiplier derived from drape coefficient
• calculate_gravity_stretch — longitudinal elongation from GSM weight, capped at 15% per patent PCT/EP2025/067317
• calculate_dynamic_alpha — transparency with sinusoidal "breathing" pulse when fit < 95%
• get_render_metrics — primary API returning width, height, alpha, is_shiny, is_scanning, patent_id

Fixes a falsy-zero bug from the reference spec: if not timestamp → if timestamp is None, which caused timestamp=0 to be silently discarded.

engine = RobertEngine()
metrics = engine.get_render_metrics("silk_haussmann", shoulder_w=450, torso_h=800, fit_score=88)
# {"width": 1062.0, "height": 803.4, "alpha": 0.85, "is_shiny": True,
#  "is_scanning": True, "patent_id": "PCT/EP2025/067317"}

New: tests/test_robert_engine.py

29 unittest cases covering constants, all three physics methods (including GSM floor/ceiling clamping, alpha floor/ceiling), end-to-end get_render_metrics, and custom fabric injection via the constructor.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
tryonyou-pilot	Error		Apr 7, 2026 1:36pm