fix(Mention): Maintain mention after nym change

[brymut]

Description

Changing nym should still point to the user mentioned instead of losing link.

fixes #2232

Screenshots

Screen.Recording.2025-09-30.at.16.55.04.mov

Checklist

Are your changes backward compatible? Please answer below:
Y

On a scale of 1-10 how well and how have you QA'd this change and any features it might affect? Please answer below:
8

For frontend changes: Tested on mobile, light and dark mode? Please answer below:
Y

Did you introduce any new environment variables? If so, call them out explicitly here:
N

Did you use AI for this? If so, how much did it assist you?
Y? but the AI suggestions required DB changes even though all we needed was already in the DB. Maybe more premium models would've come up with something better. So I just worked out this solution.

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Note

Resolve mentions to the correct user even after username changes by adding userByMention GraphQL query and wiring frontend mention/popover to use it with itemId.

• GraphQL/API:
  • Add Query.userByMention(name: String!, itemId: ID): User with resolver that resolves a user from Mention records for a given itemId, falling back to user(name).
• Frontend:
  • components/text.js: Pass itemId into mention renderer and UserPopover; dynamically link mentions to /${user.name} when resolved. Update useMemo deps to include itemId.
  • components/user-popover.js: Query USER_BY_MENTION (when itemId provided) and fall back to USER; expose resolved user to children; refine loading and display logic.
• GQL Fragments:
  • Add USER_BY_MENTION query in fragments/users.js.

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