feat: upgraded Langflow version to 1.9.0, upgraded Docling version

[lucaseduoli]

This pull request updates Langflow version to 1.9.0, and updates the DoclingManager process management in the TUI to improve reliability and simplify output handling. The most significant change is redirecting the subprocess output to a log file instead of using pipes, which prevents crashes when the parent process exits unexpectedly. The code also upgrades dependencies and streamlines output capture by tailing the log file in a single thread.

Process management and output handling improvements:

• Redirected subprocess stdout and stderr to a log file (docling-serve.log) in the TUI directory, instead of using pipes. This prevents SIGPIPE crashes and loss of in-memory state when the parent process exits. [1] [2]
• Updated the output capture mechanism to use a single thread that tails the log file, replacing the previous dual-threaded approach for capturing stdout and stderr pipes.
• Adjusted final process output reading to fetch from the log file, since pipes are no longer used.

Dependency updates:

• Upgraded docling-serve[ui] from version 1.5.0 to 1.15.1 and docling-core from 2.48.1 to 2.71.0 in the subprocess command.

Duplicate of #1355