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/src/lib/api.ts

@@ -1,4 +1,4 @@
-// Thin fetch wrapper for the podpuddle API (session cookie auth).
+// Thin fetch wrapper for the podsteadr API (session cookie auth).
 
 export class ApiError extends Error {
   constructor(public status: number, message: string) {