Make permission checking mode-aware and group missing perms by location.

- Adjust server-wide permission list to depend on settings.UseThreads to avoid reporting irrelevant missing permissions. Append standard permissions after mode-specific ones.
- In panel permission checks, treat a panel as using threads if either global settings or the panel enable threads. Use logic.ThreadPermissions for thread-mode channel checks and simplify assembled permission slices.
- Add ThreadPermissions constant in bot/logic/discordpermissions.go for reuse.
- Rewrite findMissingPermissions to return labeled missing-permission groups (panel channel, notification channel, transcript channel) instead of a flat list; check primary channel, optional notification channel (thread mode), and transcript channel, using channel-level and guild-level checks as appropriate.
- Update reply formatting to render missing permissions grouped by location with a title and footer linking docs.

These changes reduce false positives, centralize thread-mode permissions, and provide clearer error messages to users about where permissions are missing.

Replace local permission constants/usages with the centralized github.com/TicketsBot-cloud/common/botpermissions package across the codebase. Updated imports and calls to BuildPermissions to use botpermissions.StandardPermissions, MinimalPermissions, ThreadModeRequired, NotifChannelRequired, TranscriptChannelRequired, and ChannelModeRequired where appropriate. Removed duplicate permission arrays from bot/logic/discordpermissions.go and adjusted code to copy/append permission slices safely. Also enabled a local replace for the common module in go.mod. This centralizes permission definitions and reduces duplication.

Uncomment the replace directive for github.com/TicketsBot-cloud/common in go.mod to point to the local ../common module. This allows building and testing against the local copy of the common package during development; other replace directives remain unchanged.