SimpleRaidAssign

### v1.1.0 — Per-attribution announce filter

  - **Checkbox on every attribution row** controlling whether the attribution is included in the next chat broadcast. Toggling the checkbox does **not** change which attribution is loaded in the right edit panel.
  - **Master "Select all / none" checkbox** above the scroll list, automatically synced with the row state and clickable to flip everything between "all checked" and "all unchecked".
  - New attributions default to **selected** so the announce flow stays one-click when no filtering is needed.
  - Selection state is held in a module-local table and is **not persisted** to SavedVariables — it resets between sessions on purpose.
  - `Broadcast.lua` API additions: `BuildSegments` / `BuildMessages` / `Announce` / `Preview` accept an optional `filter` set (`{ [attribId] = true }`). When `nil`, the legacy "include everything" behavior is preserved.
  - The `[Announce]` and `[Preview]` buttons short-circuit with a chat message if no attribution is selected, instead of sending an empty message.