Add Kill Bill Design System 2026 tokens (assets 1.1.0)

[tungleduyxyz]

Refs killbill/technical-support#316. Land this first — all engine PRs depend on these tokens.

• New tokens.css — the single source of truth for the Kill Bill Design System 2026: 6 color primitive scales, semantic tokens (primary/surface/onSurface/outline/status/disabled/tag-containers), 16 Inter text styles as font: var(--kb-…) tokens, and a --kb-legacy-* section preserving old-theme values exactly.
• Deterministic load order in common.css (explicit requires instead of require_tree; tokens first).
• --bs-* Bootstrap bridge moved to bootstrap_and_overrides.css, right after bootstrap.min.css so it wins the cascade.
• Gem stylesheets converted — theme.css, element.css, datatable.css: ~80 hardcoded colors → tokens; stale sourceMappingURL comments and a calc(unquote(...)) artifact removed.
• README gains a "Theming / design tokens" section; version bumped 1.0.2 → 1.1.0.

Verified via assets:precompile in kaui-standalone (tokens defined once, bridge ordering correct).

[Copilot]

Copilot review overview

🟡 Changes recommended

The Bootstrap bridge is ineffective, several foreground pairs fail accessibility contrast, and DataTables duplicates a primitive color.

Review effort: Balanced
Findings: 4 · 1

Open (5)

• Bootstrap components remain on stock palette · New
• Duplicate primary color outside token source of truth · New
• Pressed primary state fails WCAG AA contrast · New
• Warning color pair fails WCAG AA contrast · New
• Ambiguous shorthand omits explicit base token · New

What changed in this PR

Adds shared Kill Bill Design System 2026 tokens and migrates existing stylesheets to consume them.

Changes:

• Introduces color, typography, semantic, and legacy tokens.
• Establishes deterministic stylesheet ordering and Bootstrap mappings.
• Converts legacy styles, documents theming, and releases version 1.1.0.

File	Description
README.md	Documents token usage and theming rules.
lib/​assets/​version.rb	Bumps the gem to 1.1.0.
app/​assets/​stylesheets/​assets/​tokens.css	Defines the design-system tokens.
app/​assets/​stylesheets/​assets/​theme.css	Replaces hardcoded theme colors.
app/​assets/​stylesheets/​assets/​jquery_datatables.css	Updates the selected-row color.
app/​assets/​stylesheets/​assets/​element.css	Migrates legacy styling to tokens.
app/​assets/​stylesheets/​assets/​datatable.css	Tokenizes legacy table colors.
app/​assets/​stylesheets/​assets/​common.css	Makes asset ordering explicit.
app/​assets/​stylesheets/​assets/​bootstrap_and_overrides.css	Adds the Bootstrap token bridge.

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[tungleduyxyz]

Addressed the Copilot review in 490306a:

• Duplicate RGB triplet — fixed: added --kb-primary-500-rgb: 21, 94, 239; channel primitive to tokens.css; jquery_datatables.css now references it (--dt-row-selected: var(--kb-primary-500-rgb);), restoring the token-only update workflow.
• Bootstrap bridge overclaim — comment corrected: Bootstrap 5.0.2's compiled component rules never read --bs-* vars, so the bridge serves var(--bs-*) consumers only; stock component theming lives in theme.css's explicit overrides (as before this PR). Extending it to stock components would need a Bootstrap upgrade (5.3+), out of scope here.
• README shorthand typo — fixed: surface tokens now listed explicitly.
• WCAG AA contrast (pressed primary ~4.3:1, warning pair ~3.5:1) — both pairs come verbatim from the Figma design source (primaryPressed/onPrimary, warning/onWarning). Rather than fork implementation from design, both are now annotated in tokens.css as known issues pending design review.