🐛 fix(limiter): reject namespace IDs starting with dash

[sodre]

Summary

• Add a guard in register_namespace() to regenerate namespace IDs that start with -, preventing Click from misinterpreting them as option flags in CLI commands like namespace recover and namespace purge
• Update CLAUDE.md to document the dash exclusion in namespace ID format
• Add unit test verifying the regeneration behavior by mocking secrets.token_urlsafe

Test plan

• Unit test test_register_namespace_skips_dash_prefixed_id passes
• Generated sync code is up-to-date (hatch run generate-sync reports unchanged)
• All 2350 unit tests pass with 100% diff coverage
• CI passes

Closes #398

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.89%. Comparing base (eca1c42) to head (5b21823).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #399   +/-   ##
=======================================
  Coverage   91.88%   91.89%           
=======================================
  Files          33       33           
  Lines        7435     7437    +2     
=======================================
+ Hits         6832     6834    +2     
  Misses        603      603           

Flag	Coverage Δ
doctest	29.43% <100.00%> (+0.01%)	⬆️
e2e	42.36% <50.00%> (+<0.01%)	⬆️
integration	50.84% <100.00%> (+0.01%)	⬆️
unit	91.62% <100.00%> (+<0.01%)	⬆️

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