Sharpen: refuse Indexed Color and Bitmap documents (#12953)

paint.sharpen and its live stroke fail with the reference application's
alert text, and a press with the Sharpen tool opens that alert, as the
Dodge tool does since #12686.

crates/engine/src/cmd/retouch_cmds/dab.rs

@@ -265,12 +265,13 @@ impl DabTool {
     }
 }
 
-/// The reference application refuses a Dodge stroke in Indexed Color and Bitmap documents, with
-/// its alert's words (#12686); other modes (Multichannel and Duotone were not measured) tone as
-/// before. The live stroke checks this too, so it previews nothing there.
+/// The reference application refuses a Dodge or Sharpen stroke in Indexed Color and Bitmap
+/// documents, with its alert's words (#12686, #12953); other modes (Multichannel and Duotone were
+/// not measured) paint as before. The live stroke checks this too, so it previews nothing there.
 fn mode_refusal(s: &Session, cmd: &str) -> Result<()> {
     let tool = match cmd {
         "paint.dodge" => "dodge tool",
+        "paint.sharpen" => "sharpen tool",
         _ => return Ok(()),
     };
     let why = match s.active().map(|st| st.doc.mode) {

crates/ui-egui/src/tools/brush_refusal.rs

@@ -19,10 +19,12 @@ pub const INDEXED: &str = "Could not use the {tool} because it does not work wit
 pub const BITMAP: &str = "Could not use the {tool} because it does not work with Bitmap images (convert image to Grayscale mode to edit).";
 
 /// The tool's name in the colour-mode alerts, for the tools whose wording was measured: the Dodge
-/// tool. Kept apart from [`tool_name`]: the layer alerts weren't measured for these tools (#12685).
+/// and Sharpen tools. Kept apart from [`tool_name`]: the layer alerts aren't wired for these tools
+/// yet (#12685, #12952).
 fn mode_tool_name(tool: Tool) -> Option<&'static str> {
     match tool {
         Tool::Dodge => Some(tl!("dodge tool")),
+        Tool::Sharpen => Some(tl!("sharpen tool")),
         _ => None,
     }
 }