feat: desktop pet plugin (/pet) -- an animated terminal dog

[piercebrookins]

What

Adds a desktop pet plugin: a tiny ASCII dog that lounges in the
bottom-right of your prompt, animates (blink + wag), and rotates fun quips
while you think. It reflects the model you've set and steps aside while the
agent works.

                    (.v.) Marshmallow  *****  | "i guarded main from a force-push" - gpt-4o

Commands

Command	Description
/pet on	Adoption picker (like /model), then summon your dog
/pet off	Hide the pet
/pet pick	Re-open the picker to swap breeds
/pet <breed>	Adopt a breed directly (e.g. /pet shiba)
/pet rename <name>	Rename your pup
/pet quip	Reroll the quip
/pet list / grid	Rarity-colored one-liner list of all 19 breeds
/pet	Status

19 breeds across 5 rarities (common -> legendary, gray -> gold).

How it's wired (no core edits)

Follows the AGENTS.md golden rule -- it's a self-contained plugin under
code_puppy/plugins/pet/, modeled on prompt_newline:

• startup -- subclasses the PromptSession used by the main input prompt
  so the pet rides along as an animated bottom_toolbar. prompt_toolkit
  renders/refreshes it itself, so it never fights the REPL or smears escape
  codes (an earlier background-thread approach did exactly that -- this is the
  fix).
• custom_command / custom_command_help -- the /pet command + help.

State (enabled / species / name) persists in puppy.cfg via the generic
config API. Styled to match the prompt palette (bright cyan / blue / green).

Notes

• Zero LLM tokens -- quips are a static list; all rendering is local.
• Fails gracefully -- a rendering hiccup never breaks the prompt.
• ruff check + ruff format clean. No command_line/ edits, no core diffs.
• Every file is well under the 600-line cap.