Clean up pre-existing mypy errors (~66 across 13 files)

[RFingAdam]

Status

CI's typecheck job is currently advisory (continue-on-error: true) because the codebase carries ~66 pre-existing mypy errors spread across 13 files. The most affected modules are analyzers/power_integrity/current_profiler.py (40+ Returning Any errors), analyzers/antenna/trace_antenna.py, parsers/step_parser.py, and server.py (3-4 isolated errors).

Acceptance criteria

• Resolve all current mypy errors under mypy src/mcp_pcb_emcopilot/ --ignore-missing-imports.
• Remove continue-on-error: true from the typecheck job in .github/workflows/ci.yml.
• CI typecheck stays green on the PR that closes this issue.

Suggested approach

Tackle by module — current_profiler.py is the biggest contributor and most of its errors are the same shape (helper functions returning Any from numpy ops; one cast() per function fixes the lot).

[RFingAdam]

Closed by PR #125 (commit 81570f0). All 66 mypy errors resolved across 13 files. continue-on-error removed from the typecheck job — mypy is now a hard CI gate.