fix(web): mark a section's nav link on its subjects' pages, not only its index

`/quantus/market/near-intents` marked nothing in the section nav, nor did a
block, account or runtime page: the nav tested the index plus a hand-kept list
of exceptions that every newer section had missed. `sectionOf` in
lib/routes.ts now answers it once, over every subject field. Block zero stays
with Genesis alone.

Closes #40

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015pkwBsR54NRmZyU4QVhvfj

web/src/components/SectionNav.tsx

@@ -15,7 +15,7 @@
 import { Link } from 'react-router-dom'
 
 import type { Window as WindowName } from '../api/generated/Window'
-import { href, isStandings, type Route, SECTIONS } from '../lib/routes'
+import { href, isStandings, type Route, SECTIONS, sectionOf } from '../lib/routes'
 
 export function SectionNav({
   chain,
@@ -31,6 +31,7 @@ export function SectionNav({
   if (!chain) return null
   // The standings are current when nothing else is: no panel open, no index.
   const onStandings = isStandings(route)
+  const current = sectionOf(route)
 
   return (
     <nav className="sections" aria-label="Section">
@@ -57,16 +58,8 @@ export function SectionNav({
           key={s.id}
           to={href({ chain, index: s.id })}
           className="section-link"
-          // A call's own page belongs to the Calls section, so the nav marks
-          // it there rather than nowhere.
-          aria-current={
-            route.index === s.id ||
-            (s.id === 'call' && route.call !== null) ||
-            (s.id === 'event' && route.event !== null) ||
-            (s.id === 'node' && route.node !== null)
-              ? 'page'
-              : undefined
-          }
+          // A subject's own page belongs to the section that indexes it.
+          aria-current={current === s.id ? 'page' : undefined}
         >
           {s.label}
         </Link>

web/src/lib/routes.ts

@@ -314,6 +314,33 @@ export function isStandings(route: Route): boolean {
   )
 }
 
+/**
+ * The section a route belongs to, for the nav to mark.
+ *
+ * A subject's own page belongs to the section that indexes it:
+ * `/quantus/market/near-intents` is in Markets as much as `/quantus/market`
+ * is. The nav used to test the index plus a hand-kept list of exceptions, and
+ * every section added after the list was written — markets, blocks, accounts,
+ * runtimes — went unmarked on its own pages. Same lesson as {@link isStandings}:
+ * one place, written over every subject field.
+ *
+ * Block zero is the exception: the nav has a Genesis link for exactly that
+ * block, and marking Blocks beside it would mark two places at once. A miner
+ * belongs to no section — the standings are its index, and they have their own
+ * link.
+ */
+export function sectionOf(route: Route): SectionName | null {
+  if (route.index) return route.index
+  if (route.block !== null) return route.block === '0' ? null : 'block'
+  if (route.account !== null) return 'account'
+  if (route.runtime !== null) return 'runtime'
+  if (route.call !== null) return 'call'
+  if (route.event !== null) return 'event'
+  if (route.node !== null) return 'node'
+  if (route.market !== null) return 'market'
+  return null
+}
+
 /** The canonical path for a route. The inverse of {@link parse}. */
 export function href(route: Partial<Route>): string {
   const chain = route.chain ?? ''