Add Pillow-based visual variant for Pirate Treasure (PirateTreasure2) with UI integration

[Appurupai3]

Motivation

• Provide a visual, Pillow-rendered variant of the existing pirate word-guessing game to improve player immersion by showing the player avatar, hanging rope, shark art and fragment effects on failure.
• Integrate the visual variant into the existing game menu and help text so users can choose between the original ASCII display and a graphical display.

Description

• Added a visual_mode option to PirateTreasureModal and introduced a new PirateTreasure2Modal that enables graphical rendering and fetches the player avatar via fetch_avatar_image.
• Implemented full Pillow-based rendering in dcrbot.pirate_game.py including image assembly helpers (_paste_circular_avatar, _draw_pirate_character, _draw_player_fragments, _build_shark_cutout, etc.), an embedded base64 SHARK_IMAGE_BASE64 asset, and render_pirate_board that returns a discord.File PNG.
• Added build_pirate_display and edit_pirate_message helpers to return/embed image attachments and updated interaction flows to attach the generated image when visual_mode is enabled.
• Updated UI: added a new 海盜寶藏2 button in GameMenu, updated build_game_help_embed descriptions, and adjusted build_pirate_embed to reflect visual mode and to suppress ASCII stage art when the graphical board is used.

Testing

• No automated tests were run for this change.

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Codex Task