feat: docs restructure, show_versions, pyright CI, remove 1e-10 zero guards

[quantbai]

Summary

• Add show_versions() for bug report diagnostics
• Add community templates (issue, PR, CODE_OF_CONDUCT, SECURITY)
• Restructure docs: CLAUDE.md (AI memo), CONTRIBUTING.md (human guide)
• Add pyright static type checking to CI pipeline
• [NUMERICAL] Remove arbitrary 1e-10 zero guards (23 instances)
• Replace interval-based panel skeleton with union-based skeleton

Change Type

• Bug fix (corrects incorrect behavior)
• New feature (new operator or functionality)
• Refactor (no behavior change)
• Numerical change (alters factor computation results) [BREAKING]

Numerical Impact

Category	Before	After
divide, inverse	abs(denom) < 1e-10 → null	No guard. Inf → null via Factor
zscore, scale, etc.	< 1e-10 → 0.0	== 0 → 0.0 (exact zero)
ts_regression, etc.	< 1e-10 → 0.0	== 0 → 0.0 (exact zero)

Eliminates silent data loss from legitimate small values.

Testing

• Added or updated tests
• All tests pass (pytest tests/ -v) -- 141 passed
• Lint passes (ruff check elvers/)
• Type check passes (pyright elvers/) -- 0 errors