[Portfolio] BattleGrid: first gameplay validation slice

[notion-portfolio-actuator]

Run the first usable BattleGrid validation slice through the governed GitHub lane.

Focus

• Run cargo run.
• Verify the happy path.
• Capture the first blocker.

Done when

• The issue exists in GitHub.
• The issue reflects the current BattleGrid validation focus.
• The actuation ledger and webhook loop confirm the write.