docs(skills): add DataLimitCounter, DataFeatureFlag, cap tables, feature flags to blueprint docs

[pyramation]

Summary

Documents the new limits/caps system in customer-facing skills.\n\nconstructive-features/SKILL.md:\n- Added cap tables, feature flags, credits entries in Multi-tenancy section\n- Added DataLimitCounter + DataFeatureFlag entries in Data Modeling section\n- Updated Data* generator count 25 → 27\n\nblueprint-definition-format.md:\n- New "Limits & Feature Flags" section with full node type reference table\n- DataLimitCounter — all data options (limit_name, scope, actor_field, events)\n- DataFeatureFlag — all data options (feature_name, scope, entity_field)\n- Prerequisites note (requires limits_module)\n- Two complete blueprint JSON examples (limit projects per org, gate table behind feature flag)\n- Updated total node type count 25 → 27\n\n## Review & Testing Checklist for Human\n\nGreen — documentation-only changes.\n\n- [ ] Verify DataLimitCounter data options match the actual SQL generator signature\n- [ ] Verify DataFeatureFlag data options match the actual SQL generator signature\n- [ ] Spot-check the blueprint JSON examples are syntactically valid\n\n### Notes\n\nPart of planning issue #799.

Link to Devin session: https://app.devin.ai/sessions/b4ff120294f446d8a0407ac21e05f7bb
Requested by: @pyramation

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