feat: persist and restore Discord member roles on rejoin

[swayam-agrahari]

Overview

Adds functionality to automatically persist a member's Discord roles when they leave the server and restore them when they rejoin.

Currently, when a user leaves and joins again, all their roles are lost and moderators must manually reassign them. This change automates that process.

How it works

• When a member leaves (GuildMemberRemoval), their role IDs are collected and saved via the Root backend.
• When the member rejoins (GuildMemberAddition), the bot fetches the stored roles and restores them automatically.

Notes

• The @everyone role is excluded since it is implicitly assigned by Discord.
• Role restoration errors (e.g., deleted roles or permission issues) are safely ignored to avoid breaking the event handler.

Related PR

This feature depends on the supporting backend changes in root:

➡ Supporting PR: pr link
Closes #93

[Copilot]

Pull request overview

This PR adds Discord role persistence across leave/rejoin events by saving a departing member’s role IDs to the Root backend and restoring those roles when the member rejoins.

Changes:

• Request the GUILD_MEMBERS gateway intent to receive member add/remove events.
• Persist role IDs on GuildMemberRemoval (excluding the @everyone role).
• Restore persisted role IDs on GuildMemberAddition via new GraphQL client methods.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 10 comments.

File	Description
src/main.rs	Captures roles on member removal and restores roles on member addition; adds GUILD_MEMBERS intent.
src/graphql/queries.rs	Adds GraphQL mutation/query helpers to save and fetch persisted member roles.

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[swayam-agrahari]

@hrideshmg pls review this : )