[cschanhniem]

Summary

• Adds FET- (Family Evidence Trail View) schema: per-family aggregation of all evidence schema references into a timeline view
• REQUIRED_TRAIL_SCHEMA_TYPES (9): BTI, BEG, SAT, PCC, BSP, SEG, ECC, RSR, PQT
• VALID_TRAIL_COMPLETENESS_GRADES: complete/partial/empty (all-present / some-present / none)
• build() deduplicates duplicate schema_type events, auto-computes grade
• dry_lab_only=True enforced; TOY- prefix blocked; empty limitations rejected
• Fixes regression test to use sys.executable instead of "python" (subprocess python was python3.14 without pytest)
• 57 tests; BASELINE 9828→9891

Test plan

• 57 unit tests pass: schema constants, build happy paths, validate rejections, format output
• Regression test passes (sys.executable fix)
• Smoke test: FET-001/FAM-001 with 3 events → grade=partial, present=[BSP,BTI,SEG]