feat(docs): standalone docs site chrome + category/subcategory navigation

Docs pages no longer embed the app Header (whose hx-post login form silently
degraded to a native GET, leaking credentials into the URL — this page never
loaded htmx). New docs-owned topbar: search, theme picker, Open App; anonymous
visitors get a plain /login link. Optional-auth middleware (hand-rolled —
echojwt's ErrorHandler return ends the chain, producing empty 200s) populates
the user for signed-in visitors.

Navigation rebuilt from the docs directory tree: 6 sections, subcategory
groups, server-rendered expansion and active states. Search results are a
templ partial (/docs/search/partial); code highlighting is server-side chroma
(previously dead hljs CSS); prose is theme-aware via typography DEFAULT vars
(prose-invert painted unreadable text under light themes). /docs renders the
index directly; standalone 404 without the tailwind CDN.

Tests: navigation routing/expansion (internal/docs), render pins asserting no
login form/password field/app sidebar ever return on docs pages.
lint-rendering: exempt *.test.ts fixtures (jsdom DOM building); docs.ts
baseline 5 -> 1.

templates/types.go

@@ -209,8 +209,20 @@ type Navigation struct {
 	Sections []NavSection
 }
 
+// NavSection is a top-level documentation category. Items are documents that
+// live directly in the section; Groups are subcategories (subdirectories).
 type NavSection struct {
 	Title     string
+	Icon      string
+	Items     []NavItem
+	Groups    []NavGroup
+	Collapsed bool
+}
+
+// NavGroup is a subcategory inside a NavSection (a subdirectory of docs).
+type NavGroup struct {
+	Title     string
+	Icon      string
 	Items     []NavItem
 	Collapsed bool
 }
@@ -218,7 +230,14 @@ type NavSection struct {
 type NavItem struct {
 	Title string
 	URL   string
-	Icon  string
+}
+
+// SearchResultItem is one entry in the docs search results partial. The
+// server renders it (templ); the client only swaps the markup in.
+type SearchResultItem struct {
+	Title    string
+	Category string
+	URL      string
 }
 
 type Document struct {