feat: ComfyUI video assistant SaaS plan + shared types cleanup

- Add plan/2026-05-18-comfyui-video-assistant-saas.md (gpt-5.5 generated)
- Add src/server/ and src/shared/ type definitions
- Update comfyui routes and api_key auth
- Remove old metapi docs, deploy/k3s, and deprecated configs

src/auth/api_key.rs

@@ -21,6 +21,7 @@ pub enum DownstreamAuthResult {
 pub async fn authorize_downstream_token(
     token: &str,
     pool: &SqlitePool,
+    global_proxy_token: Option<&str>,
 ) -> Result<DownstreamAuthResult, String> {
     // Try managed keys first
     if token.starts_with("sk-") {
@@ -36,11 +37,27 @@ pub async fn authorize_downstream_token(
             return Ok(DownstreamAuthResult::Managed { key: k });
         }
 
-        // Key not found in table
+        if global_proxy_token
+            .map(|global| !global.is_empty() && token == global)
+            .unwrap_or(false)
+        {
+            return Ok(DownstreamAuthResult::Global {
+                token: token.to_string(),
+            });
+        }
+
         return Err("Invalid API key".to_string());
     }
 
-    // Not an sk- key, can't be a downstream key
+    if global_proxy_token
+        .map(|global| !global.is_empty() && token == global)
+        .unwrap_or(false)
+    {
+        return Ok(DownstreamAuthResult::Global {
+            token: token.to_string(),
+        });
+    }
+
     Err("Invalid API key format".to_string())
 }