feat(brand): BrandWordmark renders ∆I in petrol, lifts the logo

Adds a dedicated BrandWordmark widget that splits 'Recl∆Im'
into three TextSpans and tints the middle ∆I in the petrol
signal colour. The fai_web universe uses this same accent rule
for the F∆I and Ch∆In glyphs — Recl∆Im now follows it, so
the brand stays visually coherent across every F∆I surface.

Where it lands:

  - Landing page: large DeltaMark (96 px) and BrandWordmark
    (56 px) sit on a single row, the wordmark to the right of
    the mark. The two together carry the brand identity that
    a viewer sees first when opening the app.
  - NavigationRail leading: the muted 'Recl∆Im' Text line is
    replaced with the petrol-accented BrandWordmark (18 px),
    keeping the vendor tag 'F∆I' as a small muted line under it.

widget_test.dart adapts: the literal 'Recl∆Im'-find no longer
matches because the wordmark is now three text spans, so the
test checks for BrandWordmark by type — equivalent assertion,
robust to glyph-level splits.

Signed-off-by: flemming-it <sf@flemming.it>

app/lib/widgets/brand_wordmark.dart

@@ -0,0 +1,55 @@
+import 'package:flutter/material.dart';
+
+import '../theme/reclaim_tokens.dart';
+
+/// "Recl∆Im" wordmark with the ∆I glyphs petrol-coloured — the
+/// brand rule of thumb in the fai_web universe: wherever the name
+/// stands as a brand, the ∆I tinted petrol carries the F∆I-family
+/// identity. As plain text it would all share the surrounding ink
+/// colour.
+///
+/// Pass [size] for the base font size; the ∆I scales relative.
+class BrandWordmark extends StatelessWidget {
+  const BrandWordmark({
+    super.key,
+    this.size = 24,
+    this.fontWeight = FontWeight.w600,
+    this.color,
+    this.letterSpacing = -0.5,
+  });
+
+  final double size;
+  final FontWeight fontWeight;
+
+  /// Color of the non-∆I letters. Defaults to the surface's
+  /// onSurface so the wordmark reads against whichever ink/paper
+  /// backdrop it sits on.
+  final Color? color;
+  final double letterSpacing;
+
+  @override
+  Widget build(BuildContext context) {
+    final base = color ?? Theme.of(context).colorScheme.onSurface;
+    final style = TextStyle(
+      fontSize: size,
+      fontWeight: fontWeight,
+      fontFamily: ReclaimTypography.display,
+      color: base,
+      letterSpacing: letterSpacing,
+      height: 1.0,
+    );
+    return RichText(
+      text: TextSpan(
+        style: style,
+        children: [
+          const TextSpan(text: 'Recl'),
+          TextSpan(
+            text: '∆I',
+            style: style.copyWith(color: ReclaimColors.signal),
+          ),
+          const TextSpan(text: 'm'),
+        ],
+      ),
+    );
+  }
+}