fix: resolve pre-existing clippy collapsible_match warnings

Collapse nested if blocks into match guard patterns in messages.rs
and ingest.rs to satisfy clippy::collapsible_match.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/sprout-relay/src/api/messages.rs

@@ -129,11 +129,11 @@ pub fn validate_imeta_tags(tags: &[Vec<String>], media_base_url: &str) -> Result
                         return Err("imeta duration must be a valid float".into());
                     }
                 }
-                "bitrate" => {
+                "bitrate"
                     // NIP-71 standard field: bits/sec as integer, positive
-                    if value.parse::<u64>().map_or(true, |b| b == 0) {
-                        return Err("imeta bitrate must be a positive integer".into());
-                    }
+                    if value.parse::<u64>().map_or(true, |b| b == 0) =>
+                {
+                    return Err("imeta bitrate must be a positive integer".into());
                 }
                 "image" => {
                     // NIP-71 poster frame — must be a local media URL with an image extension.

crates/sprout-relay/src/handlers/ingest.rs

@@ -727,15 +727,11 @@ fn validate_diff_event(event: &Event) -> Result<(), String> {
                     return Err("parent-commit SHA must be at least 7 hex characters".to_string());
                 }
             }
-            "branch" => {
-                if parts.len() < 3 || parts[1].is_empty() || parts[2].is_empty() {
-                    return Err("branch tag requires both source and target".to_string());
-                }
+            "branch" if (parts.len() < 3 || parts[1].is_empty() || parts[2].is_empty()) => {
+                return Err("branch tag requires both source and target".to_string());
             }
-            "pr" => {
-                if parts[1].parse::<u32>().map(|n| n == 0).unwrap_or(true) {
-                    return Err("pr number must be a positive integer".to_string());
-                }
+            "pr" if parts[1].parse::<u32>().map(|n| n == 0).unwrap_or(true) => {
+                return Err("pr number must be a positive integer".to_string());
             }
             _ => {}
         }