feat(chat-bg): redesign 19 chat backgrounds as modular per-pattern files

Same treatment as the seasonal themes: split the 502-line chatBackground.ts Record into one premium module per background under lotus/backgrounds/ (each exposes a tuned dark + light ChatBgVariants), one Opus agent per background against a shared brief. chatBackground.ts now assembles DARK/LIGHT from the modules; getChatBg is unchanged. Carbon + Aurora are kept inline as-is (user favorites); none stays the empty layer. Every redesign: layered oklch palettes, seamless tiling with worked-out tile math (integer-multiple periods; edge-wrapping inline-SVG data-URIs for circuit/hexgrid/waves/herringbone/chevron/tactical), independently-tuned dark+light (not a recolor), and low "felt-not-read" opacity so chat text stays WCAG-AA legible. The 5 animated backgrounds (rain, star drift, grid pulse, aurora flow, fireflies) each colocate a vanilla-extract keyframe .css.ts, animate only background-position for a jump-free loop, and — since getChatBg strips animation for reduced-motion — render a finished static frame too. Redesigned: blueprint, stars, topographic, herringbone, crosshatch, chevron, polka, triangles, plaid, tactical, circuit, hexgrid, waves, neon, anim-rain, anim-stars, anim-pulse, anim-aurora, anim-fireflies. Gates: tsc clean, ESLint clean, Prettier clean, build OK, 551 tests pass. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-30 20:23:54 -04:00
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+import { keyframes } from '@vanilla-extract/css';
+
+// Aurora Flow — a SLOW, gentle pan of layered soft aurora ribbons.
+//
+// The living-aurora illusion is a pure `background-position` drift: each
+// comma-separated gradient layer is authored larger than the viewport
+// (backgroundSize 200%–300%, see animAurora.ts) so there is slack to slide it
+// around. Panning several broad blurred bands by DIFFERENT
+// amounts and along DIFFERENT paths makes the ribbons appear to curl and cross
+// like real northern lights — no single layer ever moves in lockstep.
+//
+// LAYER ORDER (must match animAurora.ts exactly — one position value per layer):
+//   1. green ribbon        (drifts a wide, lazy horizontal arc)
+//   2. teal ribbon         (drifts on a slower, offset diagonal)
+//   3. violet ribbon       (drifts vertically, the "curtain" fold)
+//   4. sky/aqua highlight  (small counter-drift for shimmer)
+//   5. calm reading core   (STATIC — kept at 50% 50% so the center never moves)
+//   6. vignette            (STATIC — kept at 50% 50% so edges never move)
+//
+// SEAMLESS LOOP: every animated layer starts and ends on the SAME position
+// ('0%'/'100%' being identical sample points of the repeating gradient tile),
+// so one period returns each band to its origin with no visible jump. The two
+// static layers list their fixed position at every stop so they never pan.
+//
+// SLOW & GENTLE: paired with a long duration + ease-in-out in animAurora.ts, the
+// motion reads as a barely-perceptible breathing drift, keeping the reading
+// center calm and text crisp.
+//
+// getChatBg adds `willChange: 'background-position'` here and STRIPS the whole
+// `animation` for prefers-reduced-motion / pause-animations, at which point the
+// static `backgroundPosition` authored in animAurora.ts is what shows — already
+// a finished, gorgeous aurora.
+export const auroraFlow = keyframes({
+  '0%': {
+    backgroundPosition: '0% 30%, 100% 70%, 50% 0%, 20% 80%, 50% 50%, 50% 50%',
+  },
+  '25%': {
+    backgroundPosition: '35% 45%, 70% 55%, 55% 35%, 45% 60%, 50% 50%, 50% 50%',
+  },
+  '50%': {
+    backgroundPosition: '65% 60%, 40% 40%, 45% 70%, 70% 35%, 50% 50%, 50% 50%',
+  },
+  '75%': {
+    backgroundPosition: '35% 45%, 70% 55%, 55% 35%, 45% 60%, 50% 50%, 50% 50%',
+  },
+  '100%': {
+    backgroundPosition: '0% 30%, 100% 70%, 50% 0%, 20% 80%, 50% 50%, 50% 50%',
+  },
+});