feat(fusion_accounting_bank_rec): SCSS foundation for OWL widget

Provides design tokens (variables.scss), main bank-rec stylesheet,
AI suggestion strip + alternatives panel styling, and dark mode
overrides. CSS classes (.o_fusion_*) will be consumed by OWL components
in Tasks 28-36.

Verified: all 4 SCSS files compile via libsass; web.assets_backend
bundle picks up all 4 entries; 134/134 module tests pass.

Made-with: Cursor

fusion_accounting_bank_rec/static/src/scss/dark_mode.scss

@@ -0,0 +1,64 @@
+@import "variables";
+
+// Activated via [data-color-scheme="dark"] on body or any ancestor.
+// Mirrors Odoo's standard dark-mode trigger pattern.
+
+[data-color-scheme="dark"] .o_fusion_bank_rec {
+    background: #1f2937;
+    color: #f9fafb;
+
+    &_header,
+    &_line,
+    &_detail {
+        background: #111827;
+        border-color: #374151;
+        color: #f9fafb;
+    }
+
+    &_line {
+        &:hover { border-color: #60a5fa; }
+        &.o_fusion_selected {
+            background: #1e3a8a;
+            border-color: #60a5fa;
+        }
+
+        &_header .o_fusion_date,
+        &_body { color: #d1d5db; }
+
+        .o_fusion_attachments_badge {
+            background: #374151;
+            color: #d1d5db;
+        }
+    }
+
+    .btn_fusion {
+        background: #374151;
+        border-color: #4b5563;
+        color: #f9fafb;
+
+        &:hover { background: #4b5563; }
+
+        &.btn_fusion_primary {
+            background: #3b82f6;
+            border-color: #3b82f6;
+
+            &:hover {
+                background: #2563eb;
+                border-color: #2563eb;
+            }
+        }
+    }
+
+    // AI suggestion strip — soften background colors for dark mode
+    .o_fusion_ai_suggestion {
+        &[data-band="high"]  { background: rgba(16, 185, 129, 0.1); }
+        &[data-band="medium"] { background: rgba(245, 158, 11, 0.1); }
+        &[data-band="low"]   { background: rgba(239, 68, 68, 0.1); }
+        &[data-band="none"]  { background: rgba(156, 163, 175, 0.1); }
+    }
+
+    .o_fusion_alternatives_panel {
+        background: #1f2937;
+        border-color: #374151;
+    }
+}