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

[vdusek]

Summary

• Add .rules file containing project conventions and coding guidelines
• Create AGENTS.md, CLAUDE.md, and GEMINI.md as symlinks pointing to .rules
• 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 92.27%. Comparing base (d6bb0b4) to head (269b56d).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1767   +/-   ##
=======================================
  Coverage   92.27%   92.27%           
=======================================
  Files         156      156           
  Lines       10645    10645           
=======================================
  Hits         9823     9823           
  Misses        822      822           

Flag	Coverage Δ
unit	92.27% <ø> (ø)

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