fix: harden metadata parsers and engines; sync docs (full-repo review)

Apply fixes from a full-repo review (code, tests, docs).

Security / correctness:
- Clamp attacker-controlled PNG/caBX chunk lengths to the remaining file
  size in metadata.py and noai/c2pa.py (a malformed length no longer drives
  a multi-GB read); skipped chunks seek instead of read.
- noai/isobmff.strip_c2pa_boxes is now fail-safe on a malformed box: return
  the original bytes with a warning instead of silently truncating the tail,
  so metadata --remove can no longer emit a corrupt file.
- doubao_engine._fixed_alpha_map clamps the glyph box to the image (no crash
  on degenerate width-vs-height).
- watermark_remover._run_region_hires gates the phaseCorrelate offset on
  response and magnitude (a spurious shift no longer garbles text) and drops
  the generator after a CPU fallback (no MPS/CPU device mismatch).

Robustness:
- gemini_engine, doubao_engine, region_eraser normalize grayscale and RGBA
  inputs to BGR at the engine entry points.
- image_io.imwrite returns False on an unwritable path (matches cv2).
- invisible_engine guards a None imread result before use.
- trustmark_detector._decoder uses a double-checked threading lock.
- ctrlregen.tiling.tile_positions raises on overlap >= tile.
- humanizer chromatic shift no longer wraps opposite-edge pixels.
- identify OpenAI caveat keyed on the normalized vendor, not a substring.
- Remove the dead "visible --detect-threshold" CLI option.
- publish.yml verifies the release tag matches the package version.

Docs:
- README strength 0.05 to 0.10; .env.example HF_TOKEN marked optional;
  doubao_capture README updated to reverse-alpha-only; CLAUDE.md synced with
  the new behaviors and the batch command.

Tests: new test_security_clamp.py for the read clamp and isobmff fail-safe;
erase CLI coverage; integrity-clash rule 2 end-to-end; multi-tag EXIF
survival and cross-format strip guards; channel/size, tiling, humanizer, and
imwrite regressions. Full suite 493 passed, 2 skipped; ruff and pyright src/
clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/remove_ai_watermarks/cli.py

@@ -160,7 +160,6 @@ def main(ctx: click.Context, verbose: bool) -> None:
 )
 @click.option("--inpaint-strength", type=float, default=0.85, help="Inpainting blend strength (0.0-1.0).")
 @click.option("--detect/--no-detect", default=True, help="Detect watermark before removal.")
-@click.option("--detect-threshold", type=float, default=0.25, help="Detection confidence threshold.")
 @click.option(
     "--mark",
     type=click.Choice(["auto", *watermark_registry.mark_keys()]),
@@ -178,7 +177,6 @@ def cmd_visible(
     inpaint_method: Literal["ns", "telea", "gaussian"],
     inpaint_strength: float,
     detect: bool,
-    detect_threshold: float,
     mark: str,
     strip_metadata: bool,
 ) -> None: