refactor(addmod): allow adding all users with a specific role

[Akinator31]

This pull request adds support for specifying either a user or a role when using the "add staff" and "remove staff" commands (both slash and text commands). This allows moderators to add or remove all members of a role to/from a thread at once, with appropriate validation and feedback. The implementation includes robust parsing, error handling, and limits to prevent abuse.

The most important changes are:

Add Staff Command Enhancements

• Refactored the add staff logic to support both users and roles as targets, introducing new types (AddTarget, AddTargetParse) and helper functions like parse_add_target, members_with_role, and add_role_members_to_channel in common.rs. This enables adding all members of a role to a thread in one command, with a configurable maximum (MAX_ROLE_MEMBERS_PER_ADD).
• Updated the slash command to accept a "mentionable" (user or role) as the target, with improved argument parsing and validation, and added user feedback for various scenarios (e.g., too many members, no members in role, forbidden roles).
• Updated the text command to parse and resolve user or role IDs, fetch members for roles, and provide appropriate feedback and error handling.

Remove Staff Command Enhancements

• Added support for removing all members of a role from a thread by introducing RemoveRoleOutcome and remove_role_members_from_channel, mirroring the add staff improvements.
• Updated the remove staff slash command to accept a "mentionable" as the target, with corresponding argument and description changes.

[Copilot]

Pull request overview

This PR extends the add staff / remove staff commands (slash + text) to accept either a user or a role, enabling bulk add/remove of all members of a role to/from a ticket thread with validation, limits, and updated i18n.

Changes:

• Introduces shared target parsing (AddTarget, parse_add_target) and role-member helpers (members_with_role, bulk add/remove outcomes).
• Updates add/remove staff text and slash commands to accept a “mentionable” target (user or role) and to report success/partial/limits.
• Expands English/French translations for new outcomes and improves error messages with {error} details.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
crates/rustmail/src/i18n/language/fr.rs	Adds FR strings for role add/remove outcomes; updates help + argument descriptions; updates Discord API error message to include {error}.
crates/rustmail/src/i18n/language/en.rs	Adds EN strings for role add/remove outcomes; updates help + argument descriptions; updates Discord API error message to include {error}.
crates/rustmail/src/errors/dictionary.rs	Adds parameterized mappings for DiscordError::ApiError and CommandError::CommandFailed.
crates/rustmail/src/commands/remove_staff/text_command/remove_staff.rs	Refactors text remove-staff to accept user or role targets and handle role bulk removal + feedback.
crates/rustmail/src/commands/remove_staff/slash_command/remove_staff.rs	Refactors slash remove-staff to accept mentionable target and handle role bulk removal + followup messaging.
crates/rustmail/src/commands/remove_staff/common.rs	Adds RemoveRoleOutcome and bulk removal helper.
crates/rustmail/src/commands/add_staff/text_command/add_staff.rs	Refactors text add-staff to accept user or role targets and handle role bulk add + feedback.
crates/rustmail/src/commands/add_staff/slash_command/add_staff.rs	Refactors slash add-staff to accept mentionable target and handle role bulk add + followup messaging.
crates/rustmail/src/commands/add_staff/common.rs	Adds target parsing, guild role member resolution, and bulk add helper + max limit constant.

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[Akinator31]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Applied both review fixes in commit 0b0271e:

1. dictionary.rs:197 — Changed the catch-all _ arm to bind as err and populate the {error} param via err.to_string(), so ChannelCreationFailed, FailedToFetchCategories, and FailedToMoveChannel no longer surface the raw {error} placeholder token to users.

2. common.rs:70-80 — Replaced the single-page guild_id.members(..., None, None) call with a paginated loop using a PAGE_LIMIT const (1000), an explicit early break on empty pages, and the last user ID as the after cursor — ensuring all guild members are fetched before filtering by role.