chore: rename project from podpuddle to podsteadr

Renames the repo directory and every podpuddle/PODPUDDLE reference
across code, config, and docs to podsteadr/PODSTEADR (package names,
Docker Compose project/service/volume names, env var names, UI/RSS
strings). Existing Docker volume data (uploaded blobs, mediamtx
recordings, the server's sqlite DB and its nostr identity key) was
migrated to new podsteadr_-prefixed volumes with matching filenames
so it isn't orphaned by the rename.

frontend/package-lock.json

@@ -1,11 +1,11 @@
 {
-  "name": "podpuddle-frontend",
+  "name": "podsteadr-frontend",
   "version": "0.1.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
-      "name": "podpuddle-frontend",
+      "name": "podsteadr-frontend",
       "version": "0.1.0",
       "dependencies": {
         "hls.js": "^1.6.0",