chore: enforce text conventions and split validation hooks

[TKlerx]

Summary

• document and enforce repository text encoding/line-ending conventions
• add separate precommit and prepush validation phases
• run a medium ESLint/Python quality gate on pre-push, with full validation opt-in
• add a TypeScript function-size ratchet and document the validation split

Verification

• pnpm run check:text
• node --check scripts/check-text-conventions.mjs
• .githooks/pre-commit
• .githooks/pre-push
• git diff --check