fix(theme) + docs: dark-mode persistence, merged DEPLOYMENT, GA env clarity

.env.example

@@ -1,17 +1,13 @@
-# These are auto-set by branch on Cloudflare Workers Builds (see astro.config.mjs):
-#   main branch  → Google Analytics ON,  indexable
-#   other branch → Google Analytics OFF, robots noindex
-# Only set them below to override that locally.
+# Analytics + indexing are auto-set by branch on Cloudflare Workers Builds
+# (see astro.config.mjs): main → Google Analytics ON + indexable; other branches
+# → GA OFF + robots noindex. You normally don't set anything here.
 
-# Google Analytics 4 measurement ID (e.g. G-XXXXXXXXXX). Leave empty to disable.
-# Analytics only loads after the visitor accepts cookies in the consent banner.
-PUBLIC_GA_ID=
+# Production Google Analytics 4 ID (e.g. G-XXXXXXXXXX). Set this as a BUILD
+# variable on the production Cloudflare Worker (Workers Builds → Settings →
+# Build → Variables and Secrets), NOT as a runtime variable. Leave unset to
+# disable analytics. GA loads only after the visitor accepts the cookie banner.
+SITE_GA_ID=
 
-# Set to 1 to emit robots noindex on every page. Auto-set to 1 for non-main
-# branch builds in CI; leave empty otherwise.
+# Force robots noindex on every page (auto-set to 1 for non-main branch builds
+# in CI; leave empty otherwise).
 PUBLIC_NOINDEX=
-
-# Production Google Analytics 4 ID, injected by the deploy env (e.g. Cloudflare
-# build variable SITE_GA_ID). Consumed by astro.config.mjs on `main` builds.
-# Leave unset to disable analytics. Local dev: set PUBLIC_GA_ID above instead.
-SITE_GA_ID=