feat(web): desktop mascot ("Cluck") — egg/chick/adult tamagotchi that roams the desktop, reacts to chat/events, walks on top of windows

Implements plans/2026-07-20-desktop-mascot.md. New code under
web/src/lib/mascot/ (types/sprites/render/state/behavior/actions/
stimuli + Mascot/MascotLayer/RadialMenu/NameDialog components) plus
CC0 sprite sheets at web/public/mascot/ (chicken + Onocentaur egg pack
+ reaction bubbles). MascotLayer is inserted into Desktop.svelte after
WindowLayer; <2-line integration.

Tamagotchi: egg -> chick -> adult lifecycle persisted to
localStorage['oikos-mascot'] (debounced 300ms). Egg hatches on first
naming (no timed incubation per implementation deviation). Chick/adult
wander, peck, sleep, blink autonomously via a weighted-random FSM; the
chicken walks above windows (ground line = highest window top edge
beneath its x, recomputed each tick from wmState; rides the ground when
the window beneath is dragged).

Interaction: draggable with flutter-fall physics on release mid-air;
plain click = pet (heart bubble + happy anim); right-click opens a
rounded-button radial menu (Interact/Care/Identity/Debug nested groups)
mirroring the desktop's own right-click menu styling; auto-flips above/
left near screen edges.

Awareness: stimulus bus subscribes to chat.ts streaming, activity.ts
activityLog (knowledge-entry diff), events.ts liveEvents (critical/
signal -> alarmed, execution -> happy), with priority+cooldown gating.
Egg-stage reactions are suppressed. Reaction bubbles are anti-aliased.

Sprite loop runs at ~60fps via setTimeout (not rAF) per GraphBackground
convention, dt clamped to 100ms; position via transform: translate3d
+ will-change: transform for compositor-friendly motion. Z-index
ordering: WindowLayer z-40 < MascotLayer z-[45] < desktop context menu
z-50 < RadialMenu/NameDialog z-[60].

Docs: plan + docs/mascot/README.md (MBSE subsystem model) updated to
Implemented with a deviations note covering hatch-on-naming, PNG-sheet
art, button-column radial menu, 60fps loop, egg-reaction suppression,
and window-walking ground model. VERSION bumped 0.7.13 -> 0.8.0.

web/public/mascot/LICENSE-eggs.txt

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+Eggs
+By Onocentaur
+https://onocentaur.itch.io
+March 2021
+
+Description 
+350+ pixel art eggs for your next virtual pet/match 3/farming/holiday themed game.
+
+This pack contains:
+	⁃	Over 350 16x16px eggs.
+	⁃	32 egg designs, 11 color variants.
+	⁃	2 different cracking animations for each egg.
+	⁃	Spritesheets for each color variant and cracking pattern.
+	⁃	Transparent PNGs.
+	⁃	Template files so you can color your own eggs.
+	⁃	Bonus: Letter & Number eggs.
+	⁃	Bonus: Incubator assets (nesting box and toggle-able lamp).
+	⁃	Bonus: 12 Animal assets.  
+
+Free to use for personal & professional projects.  Attribution appreciated.  If you use these assets in your project, let me know!  I look forward to seeing what you make.

web/public/mascot/LICENSE.txt

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+
+CC0 1.0 Universal (CC0 1.0) Public Domain Dedication 
+
+The person who associated a work with this deed has dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
+You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.