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_test.go

@@ -90,6 +90,21 @@ func TestResolvePartialID(t *testing.T) {
 		Priority:  1,
 		IssueType: types.TypeTask,
 	}
+	// Test hierarchical IDs - parent and child
+	parentIssue := &types.Issue{
+		ID:        "offlinebrew-3d0",
+		Title:     "Parent Epic",
+		Status:    types.StatusOpen,
+		Priority:  1,
+		IssueType: types.TypeEpic,
+	}
+	childIssue := &types.Issue{
+		ID:        "offlinebrew-3d0.1",
+		Title:     "Child Task",
+		Status:    types.StatusOpen,
+		Priority:  1,
+		IssueType: types.TypeTask,
+	}
 	
 	if err := store.CreateIssue(ctx, issue1, "test"); err != nil {
 		t.Fatal(err)
@@ -100,6 +115,12 @@ func TestResolvePartialID(t *testing.T) {
 	if err := store.CreateIssue(ctx, issue3, "test"); err != nil {
 		t.Fatal(err)
 	}
+	if err := store.CreateIssue(ctx, parentIssue, "test"); err != nil {
+		t.Fatal(err)
+	}
+	if err := store.CreateIssue(ctx, childIssue, "test"); err != nil {
+		t.Fatal(err)
+	}
 	
 	// Set config for prefix
 	if err := store.SetConfig(ctx, "issue_prefix", "bd-"); err != nil {
@@ -149,6 +170,16 @@ func TestResolvePartialID(t *testing.T) {
 			input:       "bd-1",
 			expected:    "bd-1",  // Will match exactly, not ambiguously
 		},
+		{
+			name:     "exact match parent ID with hierarchical child - gh-316",
+			input:    "offlinebrew-3d0",
+			expected: "offlinebrew-3d0",  // Should match exactly, not be ambiguous with offlinebrew-3d0.1
+		},
+		{
+			name:     "exact match parent without prefix - gh-316",
+			input:    "3d0",
+			expected: "offlinebrew-3d0",  // Should still prefer exact hash match
+		},
 	}
 
 	for _, tt := range tests {