Fix gh-316: Prefer exact ID matches over prefix matches

The ID disambiguation logic treated 'offlinebrew-3d0' as ambiguous when
child IDs like 'offlinebrew-3d0.1' existed. Now the system:

1. Checks for exact full ID matches first (issue.ID == input)
2. Checks for exact hash matches (handling cross-prefix scenarios)
3. Only falls back to substring matching if no exact match is found

Added test cases verifying:
- 'offlinebrew-3d0' matches exactly, not ambiguously with children
- '3d0' without prefix still resolves to exact match

Amp-Thread-ID: https://ampcode.com/threads/T-5358ea57-e9ea-49e9-aedf-7044ebf8b52a
Co-authored-by: Amp <amp@ampcode.com>

internal/utils/id_parser.go

@@ -81,14 +81,41 @@ func ResolvePartialID(ctx context.Context, store storage.Storage, input string)
 	hashPart := strings.TrimPrefix(normalizedID, prefixWithHyphen)
 
 	var matches []string
+	var exactMatch string
+	
 	for _, issue := range issues {
-		issueHash := strings.TrimPrefix(issue.ID, prefixWithHyphen)
+		// Check for exact full ID match first (case: user typed full ID with different prefix)
+		if issue.ID == input {
+			exactMatch = issue.ID
+			break
+		}
+		
+		// Extract hash from each issue, regardless of its prefix
+		// This handles cross-prefix matching (e.g., "3d0" matching "offlinebrew-3d0")
+		var issueHash string
+		if idx := strings.Index(issue.ID, "-"); idx >= 0 {
+			issueHash = issue.ID[idx+1:]
+		} else {
+			issueHash = issue.ID
+		}
+		
+		// Check for exact hash match (excluding hierarchical children)
+		if issueHash == hashPart {
+			exactMatch = issue.ID
+			// Don't break - keep searching in case there's a full ID match
+		}
+		
 		// Check if the issue hash contains the input hash as substring
 		if strings.Contains(issueHash, hashPart) {
 			matches = append(matches, issue.ID)
 		}
 	}
 	
+	// Prefer exact match over substring matches
+	if exactMatch != "" {
+		return exactMatch, nil
+	}
+	
 	if len(matches) == 0 {
 		return "", fmt.Errorf("no issue found matching %q", input)
 	}