Implement backend reader infrastructure with SSR route and library access control

- Fix function signatures in reader.go (c echo.Context -> c *echo.Context)
- Replace non-existent UserHasLibraryAccess with GetUserVisibleLibraries pattern
- Implement SSR reader route in router/reader.go with proper access control
- Add inline library access checking following existing codebase patterns
- Fix ReadingProgress struct to use LastReadAt instead of CreatedAt/UpdatedAt
- Ensure all reader endpoints use consistent library access validation

This provides the backend foundation for the reader feature with proper
access control and SSR rendering capabilities.

templates/types.go

@@ -166,8 +166,7 @@ type ReadingProgress struct {
 	TotalPages  int
 	Percentage  float64
 	EpubCfi     string
-	CreatedAt   time.Time
-	UpdatedAt   time.Time
+	LastReadAt  time.Time
 }
 
 type Bookmark struct {