chore: add agent instruction files as symlinks to .rules.md

[vdusek]

Summary

• Add .rules.md file containing project conventions and coding guidelines
• Create AGENTS.md, CLAUDE.md, and GEMINI.md as symlinks pointing to .rules.md
• Update .gitignore accordingly

Test plan

• Verify symlinks resolve correctly
• Lint and type checks pass

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.85%. Comparing base (1ac00b2) to head (faf3720).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #815   +/-   ##
=======================================
  Coverage   85.85%   85.85%           
=======================================
  Files          46       46           
  Lines        2778     2778           
=======================================
  Hits         2385     2385           
  Misses        393      393           

Flag	Coverage Δ
e2e	37.07% <ø> (ø)
integration	58.60% <ø> (ø)
unit	73.39% <ø> (ø)

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