feat: add pirate instruction to created tasks

[xmtp-coder-agent]

Resolves #88

Summary

• add a fixed pirate-speaking instruction to the create-task input payload
• preserve optional configured prompt content and append the issue URL after the new instruction
• update create-task tests and README documentation to cover the new prompt structure

Verification

• bun test src/handlers/create-task.test.ts
• bun test
• bun run typecheck
• bun run lint

Note

Add pirate-speaking instruction to CreateTaskHandler prompt construction

Inserts a fixed 'Speak like a pirate in all of your responses.' instruction between the optional base prompt and the issue URL when building the initial task input in create-task.ts. The prompt is now assembled as an array filtered of empty parts and joined with blank lines.

Behavioral Change: all tasks created by CreateTaskHandler will now include the pirate instruction regardless of whether a base prompt is provided.

^{Macroscope summarized 2b89dd3. (Automatic summaries will resume when PR exits draft mode or review begins).}