Add BmMT 2026 archive framework

[devin-ai-integration]

Summary

Adds the BmMT 2026 archive at content/resources/archives/bmmt-2026/, listed alongside the other archives.

• Uploads one set of problem PDFs (one per cell, matching the BmMT 2025 archive):
  puzzle-rules.pdf, puzzle-problems.pdf, individual-problems.pdf, individual-tiebreaker-problems.pdf, team-problems.pdf, relay-problems.pdf.
• Rounds: Puzzle (Rules + Problems), Individual, Individual Tiebreaker, Team, Relay. Columns: Rules / Problems / Solutions.
• Solutions remain commented out with a Solutions coming soon! placeholder.
• Adds two award links modeled on the BMT 2025 archive: Contest Results → results.pdf and Contest Results (Online) → results-online.pdf.
• Adds: Try the BmMT 2026 Online Puzzle Round on our custom [interactive site](https://curtain-pigeon-pit.uc.ax/)!

Note: results.pdf / results-online.pdf are not in this PR yet — those two buttons 404 until the awards PDFs are added.

zola build passes.

Link to Devin session: https://app.devin.ai/sessions/d38c69314d00430fa0446cc26ecd7400
Requested by: @alphdelta

[devin-ai-integration]

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