feat(ui): ink & copper ledger retheme + analytics redesign

App-wide retheme done at the token layer: Tailwind's zinc scale is remapped
to warm ink/paper neutrals and indigo to copper in globals.css, so every
page inherits the palette. Fraunces (serif display) added for page titles
and hero figures; all figures now render in mono with tabular numerals.

Analytics page redesigned around a month spine — twelve clickable columns
scaled to each month's spend that act as hero, context, and period
navigation. Adds a 'What changed' top-movers panel vs the previous month,
replaces the 8-line category trend chart with per-category sparkline small
multiples, heat-tints the six-month ledger table, and restyles the Pareto,
pace chart, and cashflow strip. Kept: Pareto, cumulative-vs-typical pace,
drill-downs, regular/occasional split.

Insights and Merchants restyled to the same kit; chart tokens centralised
in category-colors.ts (CHART). Cleared the pre-existing lint errors in
insights (typed tooltip, removed any-casts).

src/components/sidebar.tsx

@@ -92,7 +92,7 @@ export function Sidebar() {
   const navContent = (
     <>
       <div className="p-4 border-b border-zinc-800 flex items-center justify-between">
-        <h1 className="text-lg font-semibold text-white">Finance</h1>
+        <h1 className="text-xl text-zinc-100 font-display tracking-tight">Finance<span className="text-indigo-400">.</span></h1>
         <button
           onClick={() => setOpen(false)}
           className="md:hidden p-1 rounded text-zinc-400 hover:text-white hover:bg-zinc-800"
@@ -110,10 +110,10 @@ export function Sidebar() {
             <Link
               key={item.href}
               href={item.href}
-              className={`flex items-center gap-3 px-3 py-2 rounded-md text-sm mb-0.5 transition-colors ${
+              className={`relative flex items-center gap-3 px-3 py-2 rounded-md text-sm mb-0.5 transition-colors ${
                 active
-                  ? "bg-zinc-800 text-white"
-                  : "text-zinc-400 hover:text-white hover:bg-zinc-800/50"
+                  ? "bg-zinc-800 text-zinc-50 before:absolute before:left-0 before:top-1.5 before:bottom-1.5 before:w-0.5 before:rounded-full before:bg-indigo-400"
+                  : "text-zinc-400 hover:text-zinc-100 hover:bg-zinc-800/50"
               }`}
             >
               {ICONS[item.icon]}
@@ -138,7 +138,7 @@ export function Sidebar() {
             <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M4 6h16M4 12h16M4 18h16" />
           </svg>
         </button>
-        <span className="ml-3 text-base font-semibold text-white">Finance</span>
+        <span className="ml-3 text-lg text-zinc-100 font-display tracking-tight">Finance<span className="text-indigo-400">.</span></span>
       </div>
 
       {/* Mobile drawer overlay */}