Consolidate Rev-B routing, validation, and repository cleanup

[iamdarshg]

Consolidated scope

This is the single active Rev-B hardware PR. It supersedes temporary export PRs #8 and #9.

• runs KiCad ERC, netlist export, connectivity audits, DRC, and PCB-layout audits
• regenerates both Rev-B designs in an isolated copy with the installed KiCad symbol/footprint libraries
• publishes a structured readiness summary and source bundle as workflow artifacts
• preserves known design blockers as report data instead of confusing them with CI infrastructure failures
• removes generated BEC SVG output and tracked KiCad editor-preference files
• expands .gitignore for hardware exports and transient output directories

Current hardware state

• flight-control board: routed checkpoint retained; final routing/DRC completion remains in progress
• six-channel ESC: engineered power zones/via fields retained; signal routing and final DRC remain in progress
• fabrication exports remain blocked until the reported connectivity and layout failures are resolved

The PR remains draft until both PCB designs pass the final fabrication-readiness gates.