chore(web): upgrade radius scale + introduce blue --selected token

UI polish pass — design tokens for follow-up commits.

Radius scale was visually too square at the small end. Bump up so
buttons / inputs / cards feel rounded rather than boxy:

- `--radius-sm: 6px → 8px`  (buttons, inputs, small chips)
- `--radius: 10px → 12px`  (medium containers, Recent filter pill)
- `--radius-lg: 14px → 16px`  (project cards)
- `--radius-pill: 999px` unchanged (status chips)

Introduce a separate "selected" colour so selection indicators
(card borders, focus rings) read as blue instead of fighting with
the orange brand accent that drives primary CTAs:

- `--selected: #2563eb`  (Tailwind blue-600)
- `--selected-soft: rgba(37, 99, 235, 0.16)`  (soft tint for shadows)

No selectors are migrated to `--selected` in this commit — that
happens in a later "selected state" commit so the diff stays scoped.

apps/web/src/index.css

@@ -52,11 +52,14 @@
   --shadow-md: 0 6px 24px rgba(28, 27, 26, 0.07), 0 2px 6px rgba(28, 27, 26, 0.04);
   --shadow-lg: 0 24px 60px rgba(28, 27, 26, 0.16), 0 8px 16px rgba(28, 27, 26, 0.07);
 
-  --radius-sm: 6px;
-  --radius: 10px;
-  --radius-lg: 14px;
+  --radius-sm: 8px;
+  --radius: 12px;
+  --radius-lg: 16px;
   --radius-pill: 999px;
 
+  --selected: #2563eb;
+  --selected-soft: rgba(37, 99, 235, 0.16);
+
   --serif: 'Source Serif Pro', 'Source Serif 4', 'Iowan Old Style', 'Apple Garamond', Georgia, 'Times New Roman', serif;
   --sans: -apple-system, BlinkMacSystemFont, 'Inter', 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
   --mono: ui-monospace, 'SF Mono', SFMono-Regular, Menlo, Consolas, monospace;