refactor(backend): introduce DI interfaces for testability

Replace concrete *db.Queries and *pgxpool.Pool dependencies with
db.Querier and db.TxManager interfaces across all handlers, game hub,
and auth. This enables unit testing with mocks.

- Enable sqlc emit_interface to generate Querier interface
- Add TxManager abstraction to encapsulate transactions
- Convert auth package-level functions to Authenticator struct
- Add TaskQueueInterface/TaskWorkerInterface for game.Hub
- Add initial unit tests for game logic and API handlers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 100 insertions, 0 deletions

diff --git a/backend/game/hub_test.go b/backend/game/hub_test.go
new file mode 100644
index 0000000..a8fad58
--- /dev/null
+++ b/backend/game/hub_test.go
@@ -0,0 +1,100 @@
+package game
+
+import "testing"
+
+func TestCalcCodeSize_PHP(t *testing.T) {
+	hub := &Hub{}
+	tests := []struct {
+		name     string
+		code     string
+		language string
+		want     int
+	}{
+		{
+			name:     "simple php code",
+			code:     "<?php echo 1;",
+			language: "php",
+			want:     6, // "echo1;" after stripping whitespace and "<?php"
+		},
+		{
+			name:     "php with short open tag",
+			code:     "<? echo 1;",
+			language: "php",
+			want:     6, // "echo1;" after stripping whitespace and "<?"
+		},
+		{
+			name:     "php with closing tag",
+			code:     "<?php echo 1; ?>",
+			language: "php",
+			want:     6, // "echo1;" after stripping whitespace, "<?php", and "?>"
+		},
+		{
+			name:     "php with whitespace",
+			code:     "<?php echo   1 ;  ?>",
+			language: "php",
+			want:     6,
+		},
+		{
+			name:     "non-php language",
+			code:     "print(1)",
+			language: "swift",
+			want:     8,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := hub.CalcCodeSize(tt.code, tt.language)
+			if got != tt.want {
+				t.Errorf("CalcCodeSize(%q, %q) = %d, want %d", tt.code, tt.language, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestIsTestcaseResultCorrect(t *testing.T) {
+	tests := []struct {
+		name     string
+		expected string
+		actual   string
+		want     bool
+	}{
+		{
+			name:     "exact match",
+			expected: "hello",
+			actual:   "hello",
+			want:     true,
+		},
+		{
+			name:     "trailing newline ignored",
+			expected: "hello\n",
+			actual:   "hello",
+			want:     true,
+		},
+		{
+			name:     "CRLF normalized",
+			expected: "hello\r\n",
+			actual:   "hello\n",
+			want:     true,
+		},
+		{
+			name:     "mismatch",
+			expected: "hello",
+			actual:   "world",
+			want:     false,
+		},
+		{
+			name:     "multiline match",
+			expected: "line1\nline2",
+			actual:   "line1\nline2\n",
+			want:     true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := isTestcaseResultCorrect(tt.expected, tt.actual)
+			if got != tt.want {
+				t.Errorf("isTestcaseResultCorrect(%q, %q) = %v, want %v", tt.expected, tt.actual, got, tt.want)
+			}
+		})
+	}
+}