Add waxing/waning crescent phases; fix phase-shadow double-application

moon_detect.py
- detect_moon() accepts saturated_threshold / min_roundness / max_halo_ratio
  so crescent phases (dim, non-circular arc) can be detected with relaxed
  thresholds without changing defaults for full/quarter detection.

moon_phase.py
- crescent_times_in_range(): 2-hour scan returning the UTC moment illumination
  crosses a target fraction (default 28%) on the waxing or waning side.
  Used for scheduling just like phase_events_in_range() for named phases.

moon_composite.py
- Remove _apply_phase_shadow() from composite_full_moon.  NASA SVS Dial-a-Moon
  renders already include the correct terminator, libration and earthshine for
  the exact hour; applying the shadow on top double-darkened the unlit limb on
  every non-full phase.  The function stays available for callers that need it.

moon_phase_monthly.py
- Add waxing-crescent (🌒) and waning-crescent (🌘) to PHASE_SPEC.
  Timing via crescent_times_in_range(); scheduling identical to other phases.
- CRESCENT_* tuning constants (all overridable from sky-cam.conf):
    MOON_CRESCENT_TARGET_ILLUM   default 0.28
    MOON_CRESCENT_MIN_QUALITY    default 0.35
    MOON_CRESCENT_SATURATED_THR  default 180
    MOON_CRESCENT_MIN_ROUNDNESS  default 0.15
    MOON_CRESCENT_MAX_HALO_RATIO default 12.0
- run_phase() and auto_run() branch on spec['crescent'] to use crescent
  timing and detection params.
- Atmospheric background naturally captures twilight colours (dawn for waning
  crescent, dusk/dawn for waxing) from the real east frame.

https://claude.ai/code/session_01HuJ83KvMvshiY6HxJbtMsc

moon_detect.py

@@ -78,12 +78,14 @@ def _grayscale_array(image_path: str) -> np.ndarray:
     return np.asarray(im)
 
 
-def _largest_round_blob(mask: np.ndarray) -> tuple[int, np.ndarray, np.ndarray] | None:
+def _largest_round_blob(
+    mask: np.ndarray,
+    min_roundness: float = MIN_ROUNDNESS,
+) -> tuple[int, np.ndarray, np.ndarray] | None:
     labels, n = ndimage.label(mask)
     if n == 0:
         return None
     sizes = ndimage.sum(mask, labels, range(1, n + 1))
-    # Sort blobs by size descending; check roundness on the top few
     order = np.argsort(sizes)[::-1]
     for idx in order[:8]:
         label_id = idx + 1
@@ -97,23 +99,33 @@ def _largest_round_blob(mask: np.ndarray) -> tuple[int, np.ndarray, np.ndarray]
             continue
         radius = diam / 2.0
         roundness = len(xs) / (math.pi * radius * radius)
-        if roundness < MIN_ROUNDNESS:
+        if roundness < min_roundness:
             continue
         return label_id, ys, xs
     return None
 
 
-def detect_moon(image_path: str) -> MoonDetection | None:
-    """Return MoonDetection or None if no acceptable moon is found."""
+def detect_moon(
+    image_path: str,
+    saturated_threshold: int = SATURATED_THRESHOLD,
+    min_roundness: float = MIN_ROUNDNESS,
+    max_halo_ratio: float = MAX_HALO_RATIO,
+) -> MoonDetection | None:
+    """Return MoonDetection or None if no acceptable moon is found.
+
+    saturated_threshold / min_roundness / max_halo_ratio can be relaxed for
+    crescent phases, which produce a dim, non-circular arc rather than a bright
+    near-perfect disk.
+    """
     a = _grayscale_array(image_path)
     if OVERLAY_PX > 0:
         a = a.copy()
         a[-OVERLAY_PX:, :] = 0
-    mask = a >= SATURATED_THRESHOLD
+    mask = a >= saturated_threshold
     if not mask.any():
         return None
 
-    found = _largest_round_blob(mask)
+    found = _largest_round_blob(mask, min_roundness)
     if found is None:
         return None
     _, ys, xs = found
@@ -153,12 +165,12 @@ def detect_moon(image_path: str) -> MoonDetection | None:
         yh, xh = np.where(halo_labels == halo_id)
         halo_radius = max(xh.max() - xh.min(), yh.max() - yh.min()) / 2.0
     halo_ratio = halo_radius / radius if radius > 0 else 1.0
-    if halo_ratio > MAX_HALO_RATIO:
+    if halo_ratio > max_halo_ratio:
         return None  # too much glow → probably thick cloud cover
 
     # Quality score: roundness (0..1), low halo (1 = clear, 0 = thick cloud),
     # isolation factor (1 if very isolated, less if close to other lights).
-    halo_clean = max(0.0, min(1.0, (MAX_HALO_RATIO - halo_ratio) / (MAX_HALO_RATIO - 1.5)))
+    halo_clean = max(0.0, min(1.0, (max_halo_ratio - halo_ratio) / (max_halo_ratio - 1.5)))
     iso_factor = 1.0 if isolation == float('inf') else min(1.0, isolation / 600.0)
     quality = 0.5 * roundness + 0.35 * halo_clean + 0.15 * iso_factor