images: remove generator watermark from all published art

The pale four-point star bottom-right in seven project covers and four blog
heroes is the image generator's watermark, not house style. Scrubbed via
delogo and verified numerically (peak luminance in the mark's box drops from
~100-255 to under 30 in every file); thumbnails regenerated from the cleaned
masters. The cover prompt file wrongly described the mark as part of the house
look and asked new generations to include one - corrected, with a reject-list
entry naming the mark and its usual position.

public/covers/image.md

@@ -11,14 +11,19 @@ Aspect: **3:2 landscape** (existing covers are 1600 x 1074).
 ## House style block (already inside each prompt - do not paste separately)
 
 The site's covers are dark isometric hero renders: matte dark hardware, cyan and magenta
-edge light, a subtly circuit-etched ground plane, thin atmospheric haze, one small four-point
-sparkle highlight, and generous empty space on one side so the card's title text has room.
+edge light, a subtly circuit-etched ground plane, thin atmospheric haze, and generous empty space on one
+side so the card's title text has room.
 Unlike the learn-site scene plates, covers MAY have a ground plane and atmosphere - they are
 never sliced or animated.
 
 ## Reject checklist (per candidate, before you keep it)
 
 - [ ] any text, letters, numbers, logos or UI chrome anywhere in the frame (reject hard)
+- [ ] (!) THE GENERATOR WATERMARK - a small pale four-point star, usually bottom-right at
+      roughly 88% width / 82% height. It is NOT house style; earlier covers shipped with it
+      by mistake and had to be scrubbed. Check that corner on every candidate, and never ask
+      a prompt for a "sparkle highlight" (that instruction produced a second, drawn-in star
+      that sits on the artwork and cannot be cleanly removed)
 - [ ] subject clipped by the frame edge, or centred so tightly there is no negative space
 - [ ] colours drifting warm - the palette is cyan/magenta on near-black, no orange or gold
 - [ ] photographic realism or stock-render gloss (it should read as an illustration)
@@ -65,8 +70,7 @@ whole machine exists to carry.
 
 The parts hover in stable formation rather than flying apart violently - a considered
 teardown, paused for inspection. Composition sits left of centre, leaving open dark space on
-the right third of the frame. One small four-point white sparkle highlight in the lower right,
-far from the subject.
+the right third of the frame. 
 
 ---
 
@@ -95,4 +99,3 @@ hovers in mid-transfer - small, bright, clearly in motion toward the viewer's si
 frame, the one thing the whole arrangement is delivering.
 
 Composition sits right of centre, leaving open dark space on the left third for title text.
-One small four-point white sparkle highlight in the upper right, far from the subject.