Preserve ambiguous ID forms

[bartekplus]

Summary

• preserve ID, Id, and id exactly as typed
• remove the ambiguous id → i'd contraction mapping while keeping unambiguous contraction normalization
• add unit and browser-level regression coverage and update the E2E coverage matrix

Root cause

The English contraction rule performed a case-insensitive lookup of id and then reapplied the input's case pattern. As a result, the valid initialism ID was rewritten to I'D by a default-enabled safe rule.

Because all casing forms of id are valid and contextually ambiguous, this change preserves them rather than guessing. Explicit i'd input is still capitalized to I'd by the existing pronoun-capitalization rule.

Follow-up to #365.

Validation

• bun run check
• bun run test — 1,562 passed
• bun run check:e2e:coverage
• bun run test:e2e — Chrome: 26 passed
• bun run test:e2e --platform=firefox — 26 passed
• bun run test:e2e:full — Chrome: 65 passed, 7 expected skips
• bun run test:e2e:full --platform=firefox — 65 passed, 7 expected skips