docs: update specifications

[javier-godoy]

• §1: Rewrote to describe EasyGrid as a Composite component; introduced EasyGridWrapper for the custom-grid use case; mentioned getGrid().
• §2.2: Added Default Format column to the type table; filled in yyyy-MM-dd HH:mm:ss for LocalDateTime.
• §3.1: Replaced all new EasyGrid<>(grid, Person.class) examples with new EasyGrid<>(Person.class); added an EasyGridWrapper example showing getGrid() usage; removed stale constructor signatures.
• §3.3: Added Class<V> getType() to the EasyColumn API sketch.
• §7: Updated complete example to use easyGrid.setItems(...) and add(easyGrid).