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

@@ -0,0 +1,20 @@
+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.