feat: prepare 2.2.0 with UI and execution fixes

Add dark theme, richer Markdown and readable plugin results.
Improve Android input evidence, response integrity and diagnostics.
Unify lifecycle, guidance receipts and evidence sources across clients.
Keep direct action dispatch without an added AI quota approval layer.
Align version metadata at 2.2.0 and bundle Helper 1.2.2.

Validation: 3063 backend tests before the version bump; 44 after.
Frontend: 317 tests and production build passed.

apps/showcase_ui/src/_theme.scss

@@ -0,0 +1,59 @@
+@use 'sass:color';
+
+// Light values stay beside each existing declaration as fallbacks. These shared
+// semantic overrides also reach CDK overlays mounted outside routed components.
+:root[data-theme='dark'] {
+  color-scheme: dark;
+  @each $role, $value in (
+    canvas: #0b1220,
+    surface: #111c2e,
+    surface-soft: #172337,
+    surface-raised: #1e2c42,
+    text-strong: #f1f5f9,
+    text-control: #dbe4f0,
+    text-secondary: #bdcadd,
+    text-muted: #98aac1,
+    text-faint: #8da1bb,
+    border: #2b3b52,
+    border-control: #3d506a,
+    highlight: #24344d,
+    primary-text: #8ebcff,
+    primary-soft: #152e50,
+    primary-border: #375b83,
+    exploration-text: #b7b3ff,
+    exploration-soft: #29264b,
+    exploration-border: #514a83,
+    success-text: #6ee7b7,
+    success-soft: #103b32,
+    success-border: #24634d,
+    warning-text: #fcd089,
+    warning-soft: #3b2b16,
+    warning-border: #775728,
+    error-text: #ff9ca7,
+    error-soft: #421f2b,
+    error-border: #7d3d4e,
+    info-text: #83d8f5,
+    info-soft: #153747,
+    info-border: #316479
+  ) {
+    --app-#{$role}: #{$value};
+    --app-#{$role}-rgb: #{color.channel($value, 'red', $space: rgb)} #{color.channel($value, 'green', $space: rgb)} #{color.channel($value, 'blue', $space: rgb)};
+  }
+}
+
+:root {
+  color-scheme: light;
+  background: var(--app-canvas, #f8f9fa);
+}
+
+body {
+  background: var(--app-canvas, #f8f9fa);
+}
+
+input, textarea, select {
+  color: inherit;
+}
+
+::selection {
+  background: var(--app-primary-border, #bfdbfe);
+}