Restore required CI gates

[berginj]

Root cause

Field-robustness work had been merged directly to main without passing the protected PR checks. Seven files newly exceeded the repository's 500-line baseline and 23 mechanical Flake8 violations remained. Documentation PR #8 therefore failed before tests.

Fix

• remove unused imports and one unused local
• restore required blank-line formatting
• replace one assigned lambda with a nested function
• preserve the historical TrajectoryModeApproval re-export explicitly
• add the seven already-merged oversized files to the grandfathered baseline, tied to issue Restore required CI gates after field-robustness merge #12

No pipeline algorithms or runtime behavior are intentionally changed.

Validation

• flake8 . --count --statistics: 0
• python scripts/check_file_length.py: pass, 34 grandfathered files
• python scripts/sync_schema.py --check: pass
• focused affected tests: 103 passed
• full suite: 1,262 passed / 32 skipped / 0 failed
• git diff --check: pass

Closes #12.