fix(ci): fix pyright missing import and shellcheck warning

- args.py: add type: ignore[import] to rich_argparse import so pyright
  doesn't fail in CI environments where rich_argparse is not installed
- install.sh: remove unused VENV_PYTHON variable (shellcheck SC2034)

Author: fgogolli

dev-tools/install/install.sh

@@ -158,7 +158,6 @@ else
     info "reusing existing virtual environment at ${VENV_PATH}"
 fi
 
-VENV_PYTHON="${VENV_PATH}/bin/python"
 VENV_PIP="${VENV_PATH}/bin/pip"
 
 # ---------------------------------------------------------------------------

src/orb/cli/args.py

@@ -18,7 +18,7 @@
 try:
     import rich.console as _rich_console
     from rich_argparse import (
-        RichHelpFormatter as _RichHelpFormatter,  # type: ignore[import-untyped]
+        RichHelpFormatter as _RichHelpFormatter,  # type: ignore[import-untyped,import]
     )
 
     class _TtyAwareFormatter(_RichHelpFormatter):