feat(webp): add WebP streaming and snapshot APIs

- implement WebP streaming with multipart support
- add snapshot endpoint for WebP format with quality options
- introduce WebP encoding using pure Go library without FFmpeg
- update documentation and links for new WebP features

website/api/openapi.yaml

@@ -567,6 +567,18 @@ paths:
           description: ""
           content: { multipart/x-mixed-replace: { example: "" } }
 
+  /api/stream.webp?src={src}:
+    get:
+      summary: Get stream in Motion-WebP format (multipart)
+      description: "Multipart stream of WebP frames. Pure Go encoding via [go-webp](https://github.com/skrashevich/go-webp)."
+      tags: [ Consume stream ]
+      parameters:
+        - $ref: "#/components/parameters/stream_src_path"
+      responses:
+        200:
+          description: ""
+          content: { multipart/x-mixed-replace: { example: "" } }
+
   /api/stream.ascii?src={src}:
     get:
       summary: Get stream in ASCII-art format (ANSI escape codes)
@@ -691,6 +703,55 @@ paths:
           content:
             image/jpeg: { example: "" }
 
+  /api/frame.webp?src={src}:
+    get:
+      summary: Get snapshot in WebP format
+      description: "Pure Go WebP encoding via [go-webp](https://github.com/skrashevich/go-webp). No FFmpeg or CGO required for the WebP conversion itself."
+      tags: [ Snapshot ]
+      parameters:
+        - $ref: "#/components/parameters/stream_src_path"
+        - name: name
+          in: query
+          description: Optional stream name to create/update if `src` is a URL
+          required: false
+          schema: { type: string }
+        - name: quality
+          in: query
+          description: "WebP quality (1-100, default: 75)"
+          required: false
+          schema: { type: integer, minimum: 1, maximum: 100, default: 75 }
+        - name: width
+          in: query
+          description: "Scale output width (alias: `w`). Requires FFmpeg for H264/H265 sources."
+          required: false
+          schema: { type: integer, minimum: 1 }
+        - name: height
+          in: query
+          description: "Scale output height (alias: `h`). Requires FFmpeg for H264/H265 sources."
+          required: false
+          schema: { type: integer, minimum: 1 }
+        - name: rotate
+          in: query
+          description: "Rotate output (degrees). Requires FFmpeg for H264/H265 sources."
+          required: false
+          schema: { type: integer, enum: [ 90, 180, 270 ] }
+        - name: hardware
+          in: query
+          description: "Hardware acceleration engine for FFmpeg snapshot transcoding (alias: `hw`)"
+          required: false
+          schema: { type: string }
+        - name: cache
+          in: query
+          description: "Cache duration (e.g. `5s`, `1m`). Serves cached frame if within timeout."
+          required: false
+          schema: { type: string }
+          example: "5s"
+      responses:
+        "200":
+          description: ""
+          content:
+            image/webp: { example: "" }
+
   /api/frame.mp4?src={src}:
     get:
       summary: Get snapshot in MP4 format