feat(core): declare full-screen windows and generate the canvas contract - #123

Adds full-screen windows, a third surface beside windows and HUDs. Layout targets a fixed 480x270 canvas, which a core text shader (#117) maps onto the screen from glyph runs on a client-only text display. This PR declares and compiles full-screen windows and generates the canvas contract that #117 (shaders) and #118 (Minestom session) build on. It adds no shader, session, or input behaviour.

Authoring API

• JSX: <Fullscreen name="menu" mode="unlocked" backdrop="#0b0e13">…</Fullscreen>. Raw: fullscreen({ name, mode?, backdrop?, theme?, children?, debug_name? }). List them with defineWindows({ fullscreens: [...] }).
• mode: "unlocked" (default) or "horse" (FullscreenMode).
• Interaction is allowed: regions become controls, with actions, default_action, and hover. Inventory elements (items, collections, sections, patterns, anvil), sprite slots, and region tooltip/item_model are rejected.

Canvas contract

Marker encoding. A marker is a 24-bit RGB value sent with text opacity 253:

Layers. Backdrop 0, static 1, runtime layers[i] → i + 2 (≤ 253), overlay 254, cursor 255.

GLSL (assets/minecraft/shaders/include/window_fullscreen.glsl, Part::Fullscreen):

• Canvas and mapping: WINDOW_FS_CANVAS, WINDOW_FS_DEGREES_PER_PIXEL, WINDOW_FS_EDGE_ANGLES, WINDOW_FS_SNAP_EPSILON, WINDOW_FS_BLOCKS_PER_PIXEL
• Markers: WINDOW_FS_MARKER_ALPHA, WINDOW_FS_MARKER_SIGNATURE, WINDOW_FS_KIND_{CONTENT,CURSOR,BACKDROP}, WINDOW_FS_{BACKDROP,OVERLAY,CURSOR}_LAYER
• Cursor and HUD strip: WINDOW_FS_CURSOR_SIZE, WINDOW_FS_HUD_STRIP (96 half-width, 56 tall, GUI px)
• Tables: WINDOW_FS_COLOR_COUNT, WINDOW_FS_COLORS[], WINDOW_FS_CONTROL_COUNT, WINDOW_FS_CONTROLS[] (by control index)
• Functions: window_fs_payload, window_fs_is_marker, window_fs_kind, window_fs_layer, window_fs_color, window_fs_cursor_at

Kotlin / manifest. The manifest gains fullscreens and fullscreen_canvas. Generated code: WindowFullscreenEntries.all / .canvas, WindowFullscreenDefinitions, and WindowPackData.fullscreens / fullscreenCanvas.

• FullscreenCanvasEntry: width, height, degreesPerPixel, edgeYaw, edgePitch, snapEpsilon, hitMargin, displayScale, markerAlpha, cursor (text, marker, width, height), backdrop, overlayMarker, hudHiddenWorldAge (-1_000_000_001), hudStripHeight, hudStripHalfWidth, hudMaxHealth
• FullscreenEntry: surface (kind, mode, size), static, staticMarker, slots, controls (index, x, y, width, height, action, defaultAction, hover, source), switches, art, tints, layers, markers, backdropMarker, handles
• FullscreenDefinition(manifest, name) exposes canvas and surface. The typed view is left to feat(runtime): add the full-screen session with fake-survival input and a hidden HUD #118.

Every run is net-zero from the canvas origin, so a glyph's canvas position is its position in the line. Packs without full-screen windows emit nothing new, and every existing golden hash is unchanged.

Known limits

• A static composite wider than 256 px still fails, so a full-canvas frame does not work yet.
• Markers break under text shadows, so runs must be sent without shadow.
• Debug descriptors and previews ignore full-screen windows.

Checks

• just test-rust -p window-core: pass (238 lib tests, including 4 new pipeline tests and 2 contract tests)
• just lint: pass
• just check-ts, just test-ts: pass
• just golden: all 14 cases ok (new fullscreen case)
• just gradle :runtime:compileKotlin: pass. The generated fullscreen golden Kotlin also compiles against :runtime, checked with a temporary copy that was then removed.

Closes #116
Part of #115