chore(hikes): track Rheinau + Muttertagswanderung content

src/content was untracked. Start versioning these two hikes' writing
(index.svx, track.gpx, icon.svg) and add a .gitignore that keeps source
photos out (images/, private/, root cover.*) — they're large and get
re-encoded into static assets at build time. Includes the proofreading pass
on both texts (typos, grammar, gender/agreement). Other hikes stay untracked.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.85.0",
+	"version": "1.85.1",
 	"private": true,
 	"type": "module",
 	"scripts": {