feat(sagi): custom pets — Codex pet bundles, images, featured downloads

The mascot can wear a pet. Right-click it for Hide pet, Size (48-250
px), Choose pet (Sagi, featured, your own - deletable), Upload your
own..., Import .codex-pet bundle..., Find more on codex-pets.net and
Pet settings.... The worn pet and its size are viewer prefs
(agenthub.pet, agenthub.pet.size); the pets live on the server under
<data dir>/pets/<id>/ (server/lib/pets.js, /api/pets).

A Codex pet is the .codex-pet.zip format: pet.json + a 1536x1872
spritesheet.webp, 8x9 frames of 192x208, one row per state.
PetSprite.tsx plays the row of the mascot's mood; an uploaded image
bobs. Only the two bundle files are read, sizes are checked from the
zip directory before inflating, the sheet's WebP header must match,
uploads are raster only (no SVG), ids are made by the server, every
write is same-origin.

The four featured pets (Goku, Bac Ho, Border Collie, 11) are
codex-pets.net uploads with no redistribution licence, so none is
bundled: a pick downloads it from codex-pets.net by a fixed id.

docs/API.md

@@ -2267,6 +2267,23 @@ The stored key is only ever sent to the endpoint it was stored against. A blank
 
 `PATCH` rewrites the profile's files that exist (a live Claude session reads its file again; the next Codex session gets the new layer) and `DELETE` removes both. Workspaces no longer carry a router: `POST /api/lanes/:id/router/apply` is gone, and at every start the server takes the eight keys an older build wrote into a workspace's `.claude/settings.local.json` back out and clears `lanes.router_profile` (a file that is not valid JSON is left alone and retried next start).
 
+### Pets (the mascot's custom pets)
+
+```
+GET    /api/pets                      { pets, featured, sheet } — your pets, the featured list (with `installed`), the atlas geometry
+GET    /api/pets/:id/sprite           A pet's spritesheet (image/webp) or image, raster only, `nosniff`
+POST   /api/pets/import               A `.codex-pet.zip` — raw body (application/octet-stream), ≤ 8 MB
+POST   /api/pets/upload?name=<file>   One PNG, JPEG, GIF or WebP image — raw body, ≤ 4 MB
+POST   /api/pets/featured/:id         Download a FEATURED pet from codex-pets.net into this install
+DELETE /api/pets/:id                  Delete a pet (its folder under the data dir)
+```
+
+The mascot (Sagi) can wear a pet: right-click it for **Hide pet**, **Size** (48–250 px), **Choose pet** (Sagi, the featured pets, your own — deletable), **Upload your own…**, **Import .codex-pet bundle…**, **Find more on codex-pets.net** and **Pet settings…** (Settings → General → Sagi). Which pet is worn and its size are viewer preferences in `localStorage` (`agenthub.pet`, `agenthub.pet.size`); the pets live on the server, one folder each under `<data dir>/pets/<id>/` with a `meta.json` AgentHub writes.
+
+A **Codex pet** is the `.codex-pet.zip` format Codex Desktop uses (the bundles shared on codex-pets.net and in `mileson/codex-pets`): `pet.json` (`id`, `displayName`, `description`, `spritesheetPath`) and `spritesheet.webp`, a 1536×1872 atlas of 8 columns × 9 rows of 192×208 frames — idle, run right, run left, waving, jumping, failed, waiting, running, review, with 6/8/8/4/5/8/6/6/6 frames. The mascot plays the row of its mood (an agent working → running, waiting for you → waiting, an error → failed, a finished turn → jumping, idle/asleep → idle). Only the two files are read, at the archive root or one folder deep; an entry's size is checked from the zip's directory before it is inflated; the sheet must be a WebP of exactly that size (`400 EBADPET` otherwise). An uploaded image is shown still and bobs; SVG is refused because an SVG served from the dashboard's origin runs script.
+
+**Featured pets are downloaded, never bundled.** The four offered (Goku, Bac Ho, Border Collie, 11) are other people's uploads to codex-pets.net with no licence to redistribute them, so AgentHub ships none of their art: `POST /api/pets/featured/:id` takes only an id from the fixed list in `server/lib/pets.js` (`404 ENOPET` for any other, with no request made) and fetches `https://codex-pets.net/api/pets/<id>` and `/spritesheet` — no URL from the request, no redirects followed. A pet id is always made by the server (`p-<12 hex>` for an upload, `cp-<featured id>`), every write is same-origin (`403 EBADORIGIN`), and at most 50 pets are kept (`409 ETOOMANY`). Other errors: `413 ETOOBIG`, `502 EFETCH` (codex-pets.net unreachable or refusing).
+
 ---
 
 ## WebSocket API