Register the Qwen 千问AI生成 visible text mark

Calibrated on the 117-frame TC260-producer cohort (vendor_cohort_harvest +
vendor_mark_calibrate, both committed here): per-mark 2-rung ladder
(0.78, 1.27) for the two measured size modes, fitted locate box (the mark
sits ~0.025 of the short side off the edge; doubao's box clipped the first
glyph), measured template aspect 0.26, gate 0.45 (clean p99 0.301).
Strict-only (the sub-gate band is non-Qwen banners), no rival margin
(0 cross-fires on 400 doubao / 298 jimeng / 286 clean frames).
83/83 real marks detector-clean after cv2 fill.

TextMarkConfig gains a per-mark ladder field; the shipped 3-rung default
is unchanged for every other mark.

src/remove_ai_watermarks/cli.py

@@ -430,7 +430,7 @@ def _no_visible_mark_exit(source: Path) -> NoReturn:
     """Explain why no visible watermark was removed, then exit non-zero.
 
     The visible registry handles only known visual marks (the Gemini sparkle and
-    the Doubao/Jimeng/Samsung text strips). Most real uploads carry no such mark
+    the Doubao/Jimeng/Qwen/Samsung text strips). Most real uploads carry no such mark
     -- frequently an invisible/metadata watermark instead (e.g. an OpenAI or
     Gemini image whose only signal is C2PA + SynthID). Returning the input
     unchanged with exit 0 reads as success to a caller and re-serves the
@@ -692,7 +692,7 @@ def cmd_visible(
 ) -> None:
     """Remove a known visible AI watermark from an image.
 
-    Finds a known mark in its usual place (Gemini sparkle / Doubao-Jimeng-Samsung
+    Finds a known mark in its usual place (Gemini sparkle / Doubao-Jimeng-Qwen-Samsung
     text) via the watermark registry and removes it by LOCALIZING the mark to a mask
     and filling that mask with the chosen ``--backend`` (auto: best available, LaMa >
     MI-GAN > cv2). ``--mark auto`` removes every detected mark in one