Add laptop-friendly non-imaging tutorial notebooks

[Copilot]

Created lightweight, laptop-runnable tutorials demonstrating an end-to-end non-imaging NITRATES analysis on the bundled sample data, including setup and likelihood scan to extract candidate basics.

• Tutorial notebooks
  • 00_nonimaging_setup.ipynb: points NITRATES_RESP_DIR to the bundled responses, previews trigger metadata, and plots a quick-look light curve with explicit preview constants.
  • 01_end_to_end_nonimaging.ipynb: runs a minimal likelihood workflow (background + source), scans short windows, and reports amplitude, sqrtTS, and flux; clarifies solver output handling and uses an explicit amplitude floor constant.
• Documentation
  • README links to the two quickstart notebooks for non-cluster usage.

Example (window scan snippet):

AMPLITUDE_FLOOR = 1e-10  # small positive floor to avoid log(0)
def evaluate_window(t0, duration):
    t1 = t0 + duration
    sig_llh_obj.set_time(t0, t1)
    bf_vals, nllh, _ = sig_miner.minimize()
    best_vals = np.atleast_1d(bf_vals[0])  # scipy wrapper returns [array([...])]
    amp = float(best_vals[0])
    bkg_nllh = -sig_llh_obj.get_logprob({'A': AMPLITUDE_FLOOR})
    return {'duration': duration, 'amplitude': amp,
            'sqrtTS': np.sqrt(2.0 * (bkg_nllh - nllh[0]))}

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