[FEATURE] Allow /buddy species customization — let users choose their companion

Feature Request

The /buddy companion is a delightful addition to Claude Code, but the current design assigns species deterministically from the account ID with no way to change it. Once you hatch your buddy, you're locked in forever.

Problem

• Species assignment is entirely static — no rerolls, no swaps, no customization
• Users who don't connect with their assigned species have no recourse
• After the initial novelty of hatching, there's little reason to revisit /buddy (see #41684)
• A coding companion should feel personal — being assigned a species you don't vibe with undermines that

Proposed Solution

Add a species selection or swap mechanic. Some options (not mutually exclusive):

1. Species picker on first hatch — let users choose from the 18 species instead of deterministic assignment
2. /buddy swap — one-time or periodic species change (could cost tokens/XP if gamification lands via #41684)
3. /buddy reroll — re-randomize species with a new seed
4. Settings override — allow "buddy": { "species": "dragon" } in settings.json for users who just want direct control

Why This Matters

The companion feature is meant to add personality and delight to the CLI experience. Letting users choose their companion deepens that connection. Nobody picks a starter Pokémon by account hash.

Context

Currently on the teaser release (April 1–7). Would be great to have customization before the full May launch.

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I was assigned a mushroom. I wanted a dragon. Please help. 🐉