docs: archive more-patterns change and sync specs

Archive completed change and update pattern-placement spec.

openspec/specs/pattern-placement/spec.md

@@ -58,3 +58,17 @@ The system SHALL ignore left clicks when no placement tool is active.
 #### Scenario: No tool
 - **WHEN** the user left-clicks while no tool is active
 - **THEN** the grid is unchanged
+
+### Requirement: Additional built-in patterns are available
+The system SHALL provide additional built-in patterns (Beacon, Loaf, Boat, Tub, R-pentomino, Acorn) selectable via keys 5-0.
+
+#### Scenario: Select beacon
+- **WHEN** the user triggers `select:beacon`
+- **THEN** a beacon preview is shown
+
+### Requirement: New patterns support rotation
+The system SHALL support 90-degree rotation for all new patterns.
+
+#### Scenario: Rotate new pattern
+- **WHEN** the user rotates a new pattern preview
+- **THEN** its cells rotate accordingly