fix(clip_manager): retire argparse CLI in favor of corridorkey

[mountarreat]

What does this change?

clip_manager.py still shipped an argparse __main__ block that
predates the Typer migration in PR #67. The wizard action
immediately raised
NotImplementedError("interactive_wizard is not yet implemented")
at clip_manager.py:1046, because the wizard implementation had
already moved to corridorkey_cli.py::interactive_wizard in
commit e54abc8. The other three actions (list,
generate_alphas, run_inference) still worked but were
redundant with the corridorkey console script.

The README.md also actively documented the stale invocations:

uv run python clip_manager.py --action wizard --win_path "V:\..."
uv run python clip_manager.py --action run_inference --device cpu
uv run python clip_manager.py --action list 2>&1 | grep ...
CORRIDORKEY_BACKEND=mlx uv run python clip_manager.py --action run_inference

Any user following the README to run the wizard through
clip_manager.py hit the NotImplementedError immediately. The
README also had two uv run python corridorkey_cli.py wizard --win_path ... stanzas that combined a non-console-script
invocation with flags that never existed on the Typer wizard
(--win_path was an argparse artifact; the Typer wizard takes
path as a positional argument).

This PR:

• Replaces the argparse __main__ block in clip_manager.py
  (lines 1006-1046) with a small deprecation stub that prints
  a migration guide to stderr and exits non-zero. Users with
  existing scripts or cron jobs that invoke
  python clip_manager.py --action ... now see a clear
  explanation and a one-to-one mapping to corridorkey
  subcommands instead of the old NotImplementedError.
• Removes the now-unused import argparse from line 3.
• Rewrites six stale README.md stanzas to use the
  corridorkey console script and the correct Typer syntax.
• Updates the backend override section header from
  "Override via CLI flag (corridorkey_cli.py)" to
  "Override via --backend flag (on run-inference)", so
  the section reflects reality (the flag is a run-inference
  option, not a global).

clip_manager.py remains the pipeline/library module for
generate_alphas, run_inference, run_videomama,
scan_clips, etc. Only the script entry point is retired.
docs/LLM_HANDOVER.md prose still refers to clip_manager.py
as "the user-facing Command Line Wizard"; that drift belongs
to the broader documentation-consolidation work and is
deliberately out of scope for this PR.

How was it tested?

• uv run ruff format --check: clean
• uv run ruff check: clean
• uv run pytest -q --tb=short -m "not gpu": 363 passed, 1
  skipped (MLX), 4 deselected (GPU), 2 warnings. Same count
  as upstream. Both warnings are pre-existing on main and
  not introduced here.
• uv run python clip_manager.py: prints the migration guide
  to stderr, exits 2.
• uv run corridorkey --help: exits 0.
• Typer command and option syntax for each rewritten README
  command cross-checked against corridorkey_cli.py source.

Checklist

• uv run pytest passes
• uv run ruff check passes
• uv run ruff format --check passes