Fix file browser crash on non-regular files and connection leaks

- envd: reject non-regular files (devices, pipes, sockets) in GetFiles
  to prevent infinite reads from /dev/zero, /dev/urandom etc.
- host agent: add context cancellation check in ReadFileStream loop
  with proper Connect error codes
- frontend: abort in-flight file reads on file switch, directory
  navigation, and component teardown via AbortController
- frontend: guard against abort errors surfacing in UI, use try/finally
  for fileLoading state

envd/internal/api/download.go

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: Apache-2.0
+// Modifications by M/S Omukk
 
 package api
 
@@ -106,6 +107,17 @@ func (a *API) GetFiles(w http.ResponseWriter, r *http.Request, params GetFilesPa
 		return
 	}
 
+	// Reject anything that isn't a regular file (devices, pipes, sockets, etc.).
+	// Reading device files like /dev/zero or /dev/urandom produces infinite data
+	// and will exhaust memory on all layers of the stack.
+	if !stat.Mode().IsRegular() {
+		errMsg = fmt.Errorf("path '%s' is not a regular file", resolvedPath)
+		errorCode = http.StatusBadRequest
+		jsonError(w, errorCode, errMsg)
+
+		return
+	}
+
 	// Validate Accept-Encoding header
 	encoding, err := parseAcceptEncoding(r)
 	if err != nil {