feat(gemini-cli): use stream-json output and re-use session

Switch from plain text output to --output-format stream-json for
structured NDJSON events with usage stats. Capture session_id from
the init event and use --resume on subsequent turns so only the
latest user message is sent instead of re-sending full history.

Fix: redirect child stdin to /dev/null to prevent the CLI from
blocking on inherited terminal stdin (the -p flag appends to stdin
input, so an open TTY caused hangs during configure).

We can't persist process like claude code as there is no
--input-format stream-json support in gemini cli yet.

Change-Id: Idbc714ec1ac15426e486011551bcf3ad28f7f96a
Signed-off-by: rabi <ramishra@redhat.com>

Author: rabi