feat: batch-score commits after L1 scan and fix duplicate board assigment

[rmyers]

Refactor webhook handler to collect created commits and score them in batch after L1 scan completes, replacing per-commit AddCommit calls during the processCommits loop.

Webhook handler changes:

• scheduleL1Scan now receives createdCommits and calls AddCommit for each after the scan finishes (instead of during the per-commit loop)
• If scanner is not configured, commits are scored synchronously (same pre-existing behavior, no regression)
• L1 scan timeout reduced from 5min to 1min
• Removed inline AddCommit calls from processCommits

Scanner changes:

• Removed gameService dependency (no longer needed after removing RefreshPlayerAfterScan at end of RunScan)
• Simplified NewScanner constructor

Game service:

• Fixed assignPlayerBoards to skip re-assigning a board that's already in one of the player's 3 slots (previously, multiple commits from the same project could fill slots 1, 2, and 3 with the same board)
• Removed RefreshPlayerAfterScan (now handled by webhook handler)
• Added test for duplicate board assignment fix

Infrastructure:

• Added .kilo/ config (Kilo AI skills symlink)

Closes: #239