Add circuit schematics for all hardware revisions

Export PDF schematics to PNG for RS-UV3 Rev C, Rev D, RS-UV3A
Rev A, and RS-UVPA Rev E. Ordered chronologically (C→D→A).
New reference/schematics page with sidebar navigation.

astro.config.mjs

@@ -62,6 +62,7 @@ export default defineConfig({
 							],
 						},
 						{ label: 'Connectors', slug: 'reference/connectors' },
+						{ label: 'Schematics', slug: 'reference/schematics' },
 						{ label: 'Hardware Revisions', slug: 'reference/hardware-revisions' },
 					],
 				},