Fix heatmap date positioning by removing manual scale domain and using timeUnit date instead of utcdate

Co-authored-by: danmarshall <11507384+danmarshall@users.noreply.github.com>

Author: Copilot

packages/web-deploy/json/habit-tracker-complete.idoc.json

@@ -524,12 +524,9 @@
                 "encoding": {
                     "x": {
                         "field": "date",
-                        "timeUnit": "utcdate",
+                        "timeUnit": "date",
                         "type": "ordinal",
                         "title": "Day of Month",
-                        "scale": {
-                            "domain": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]
-                        },
                         "axis": {
                             "labelAngle": 0,
                             "format": "%e"
@@ -580,20 +577,17 @@
                 "encoding": {
                     "x": {
                         "field": "date",
-                        "timeUnit": "utcdate",
+                        "timeUnit": "date",
                         "type": "ordinal",
                         "title": "Day of Month",
-                        "scale": {
-                            "domain": [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]
-                        },
                         "axis": {
                             "labelAngle": 0,
                             "format": "%e"
                         }
                     },
                     "y": {
                         "field": "date",
-                        "timeUnit": "utcmonth",
+                        "timeUnit": "month",
                         "type": "ordinal",
                         "title": "Month",
                         "axis": {