PR #36: Fix onboarding validation bugs and add meta-platform schema

[Copilot]

Four pre-existing test failures in test_onboarding_check.py caused by mismatched thresholds, incomplete regex patterns, and unsafe dataclass serialization. Also adds pr36_schema.py — the PR #36 meta-platform integration schema following the established pr35_schema.py pattern.

Bug fixes in toolkit/oe/onboarding_check.py

• Partial threshold off-by-one: validate_artifact_structure classified artifacts with 4 missing fields (out of 7 required) as "invalid" instead of "partial". Changed <= 3 → <= 4.
• Missing directory pattern: "Directories scanned: 10" format was not matched. Added r"directories?\s+scanned[:\s]+\d+" to dir_patterns.
• Narrow artifact discovery: identify_candidate_artifacts used re.match (anchored), so "full_onboarding.md" was missed. Added r".*onboard.*\.(md|txt|json|yaml|yml)$" to catch "onboard" anywhere in the filename.
• asdict() on non-dataclasses: save_stage_outputs called dataclasses.asdict() unconditionally on list items, crashing on plain strings/dicts. Added is_dataclass() guard before calling asdict().

New: pr36_schema.py + tests/test_pr36_schema.py

Implements the 7-section PR #36 schema (same structure as pr35_schema.py):

Section	Content
1	Initialization — depends on PRs #16, #22–#24, #26, #32, #34, #35
2	Delta mapping — 3 new modules, 5 deltas from #35
3	Constraint integration — all 8 Yeshua axioms + 4 platform weakness inversions
4	Verification hooks — SHA-256, float elimination, ontology registry, agape accommodation
5	Agent enforcement — 2 new agent types, 7 enforcement directives
6	Serialization — canonical JSON + seed infrastructure (seed_value=36, target=1B LOC)
7	Audit/execution — 8 halting criteria, cross-PR coverage map, verification matrix

60 tests cover all sections; all pass.

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