Blank Canvas 3 - Incorrect color value fix & increased widths (#6726)

* Added Page template and typo updates

- Page template added, with singular.html removed for the purpose of single.html having post meta, and page to be plain.
- Heading size fixes

* Missing color fix & increased widths

- Assigned the correct color for text
- Wide and content widths are slightly increased for better support for Pattern Assembler

* Fix theme uri

Fixed theme uri was misplaced with previous commit, this one fixes it

blank-canvas-3/theme.json

@@ -33,8 +33,8 @@
             ]
 		},
 		"layout": {
-			"contentSize": "650px",
-			"wideSize": "1000px"
+			"contentSize": "700px",
+			"wideSize": "1160px"
 		},
 		"spacing": {
 			"spacingScale": {
@@ -240,7 +240,7 @@
 		},
 		"color": {
 			"background": "var(--wp--preset--color--base)",
-			"text": "var(--wp--preset--color--contrast)"
+			"text": "var(--wp--preset--color--foreground)"
 		},
 		"elements": {
 			"button": {