v0.8.0 — Jimeng support, Doubao fix, reproducible masks

Visible watermark removal: Jimeng support, Doubao fix, reproducible mask build

New

• Jimeng / Dreamina (即梦AI) visible wordmark removal — remove-ai-watermarks visible --mark jimeng (or --mark auto). Reverse-alpha against a captured alpha map plus a thin residual inpaint, NCC-aligned across resolutions. (#13)

Fixed

• Doubao "豆包AI生成" removal left a readable outline on real images. The detector was fooled by the thin outline (so it reported success) while the mark stayed visible to the eye. Rebuilt the alpha map (careful gray-self solve), always NCC-align, thin residual inpaint, and a wider locate box now reduce it to faint texture-level traces.

Changed

• Gemini sparkle assets rebuilt from our own controlled captures (validated NCC 0.9998 vs the prior third-party asset); removal behaviour unchanged.
• New scripts/visible_alpha_solve.py reproducibly rebuilds all three visible-mark alpha assets from committed solid-colour captures.
• Clarified SynthID labelling in identify ("SynthID watermark, inferred from C2PA metadata").