feat(video-gen): add Wan 2.7 FAL video family (t2v + i2v)

Adds Alibaba's Wan 2.7 to FAL_FAMILIES: fal-ai/wan/v2.7/{text,image}-to-video.
1080p/720p, integer duration 2-15s, negative prompts, seed, native auto audio
(no generate_audio key), i2v drops aspect_ratio (schema omits it).
Schema verified against fal.ai llms.txt + OpenAPI. $0.10/s (720p), $0.15/s (1080p).

plugins/video_gen/fal/__init__.py

@@ -111,6 +111,12 @@ FAL_FAMILIES: dict[str, dict[str, Any]] = {
                              "alibaba/wan-3.0-prime/text-to-video", "alibaba/wan-3.0-prime/image-to-video", image_param_key="start_image_url",
                              duration_int=True, audio_param_key="audio", aspect_ratios=("16:9", "4:3", "1:1", "3:4", "9:16"),
                              resolutions=("480p", "720p", "1080p"), durations=(2, 30), audio=True, seed=True),
+    # Wan 2.7: integer duration enum 2..15, aspect_ratio on t2v only (i2v follows the image), `seed` + `negative_prompt` on both;
+    # audio is auto-generated when no audio_url is given (no toggle key).
+    "wan-2.7": _family("Wan 2.7", "~60-180s", "premium", "Alibaba. 1080p, auto audio, multi-shot prompts, 2-15s.",
+                       "fal-ai/wan/v2.7/text-to-video", "fal-ai/wan/v2.7/image-to-video", duration_int=True, image_drop_keys=("aspect_ratio",),
+                       aspect_ratios=("16:9", "9:16", "1:1", "4:3", "3:4"), resolutions=("720p", "1080p"), durations=(2, 15),
+                       audio_native=True, negative=True, seed=True),
     # v1.1 publishes the full schema: integer duration 3-15, nine aspect ratios (t2v only — i2v follows the image), 720p/1080p,
     # `seed` on both endpoints, audio always on (no generate_audio key).
     "happy-horse": _family("Happy Horse 1.1", "~60-120s", "premium", "Alibaba flagship. 1080p, native audio + multilingual lip-sync, 3-15s, nine aspect ratios.",
@@ -355,7 +361,7 @@ class FALVideoGenProvider(VideoGenProvider):
 
     def get_setup_schema(self) -> dict[str, Any]:
         return {"name": "FAL", "badge": "paid", "env_vars": [{"key": "FAL_KEY", "prompt": "FAL.ai API key", "url": "https://fal.ai/dashboard/keys"}],
-                "tag": "LTX 2.3/2.5, Pixverse, Seedance 2.0/2.5/Mini, Veo 3.1, MiniMax H3, FLUX 3, Kling 3.0/4K/O3, Wan 3.0, Happy Horse, Grok Imagine, "
+                "tag": "LTX 2.3/2.5, Pixverse, Seedance 2.0/2.5/Mini, Veo 3.1, MiniMax H3, FLUX 3, Kling 3.0/4K/O3, Wan 2.7/3.0, Happy Horse, Grok Imagine, "
                        "Gemini Omni — text-to-video & image-to-video"}
 
     def capabilities(self) -> dict[str, Any]: