Add emoji suggestions to page editor

[shobhit-seg]

Summary

• suggest emoji conversions when users type supported emoticons such as :)
• support Enter and click selection without auto-replacing typed text
• skip suggestions inside inline code and code blocks
• add tests for supported mappings and unknown input

Validation

• pnpm --filter @notdrive/web test
• pnpm --filter @notdrive/web typecheck
• pnpm exec biome check on changed files
• pnpm --filter @notdrive/web build
• live browser check for :) to 🙂 conversion