fix(quickadapter): track exact label availability (#113)

fix(quickadapter): track exact label availability (#113)

Record the exact row where each Zigzag label becomes final, include TA-Lib NATR warmup/backfill in label provenance, leave unresolved trailing labels unavailable, compose centered smoothing availability over the complete kernel support, keep the incomplete right smoothing edge unavailable, reject circular wrap smoothing in causal mode, and preserve the public nine-element zigzag() tuple API.

Adds a per-row known_at_lookahead availability channel for labels and weights (weight availability lags the label by one pivot), with an optional local Gaussian fill band; the causal purge folds label and weight availability row-wise. Default path (strategy=none, fill=zero) stays byte-identical; the knn/neighbors>=2 residual is bounded, non-default, and documented.