Prompt optimizer plugin for DeepSeek Harness

Key features

• Button rendered under the composer (via the conversation.composer.dock slot)
• Reads the current composer text on click
• Rewrites the draft through the host's ctx.llm with a fixed six-step procedure (intent → context → hidden constraints → gaps → restructure → language check)
• Before/after dialog with a Replace into input button that writes the result back
• Output always matches the input language