v0.39.0 — per-call image safety flags + TTS voices

Continues the #59 agent-toolset epic (kimi-k3 field feedback).

• #61 — venice_image now exposes safe_mode and hide_watermark on its tool schema, so an agent can toggle them per generation (parity with venice_image_edit's no_safe_mode). Precedence: model arg > defaults.image.* config (#58) > hardcoded default.
• #64 — venice_model_details now returns a curated voices field (model_spec.voices, the TTS voice-id list; null for non-voice models), so an agent can pick a valid venice_tts voice without guessing.

Closes #61, #64. 504 tests green.