feat(kol): add selection-based AI optimize for prompt editor

Trigger an AI optimize panel from a text selection in the KOL prompt
editor, accept a user instruction, and stream a preview before replacing
the selected fragment. Extend the shared editor AI assist panel with
boundary-aware placement so it can be hosted inside scoped surfaces, and
update the backend optimize prompt to honor the user instruction.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/tenant/app/kol_assist_runtime.go

@@ -115,8 +115,13 @@ func BuildKolAssistUserPrompt(req AssistRequest) (string, error) {
 			}
 			schemaJSON = string(payload)
 		}
+		instruction := strings.TrimSpace(req.Description)
+		if instruction == "" {
+			instruction = "Make the prompt clearer, more complete, and easier for another AI to follow."
+		}
 		return fmt.Sprintf(
-			"Optimize the following prompt. Keep variable placeholders intact. Current schema: %s\n\nPROMPT:\n%s",
+			"Optimize the following prompt according to the instruction. Keep variable placeholders intact.\n\nInstruction:\n%s\n\nCurrent schema: %s\n\nPROMPT:\n%s",
+			instruction,
 			schemaJSON,
 			req.CurrentContent,
 		), nil