feat(12.2-02): add the datepicker field with server-side bounds and date list columns

- type: datepicker compiles the D-20 keys; format maps to displayFormat with WinterCMS's momentFormat table
- boot fails when the mode does not match the column's Go type (time.Time, lagoon.Date, lagoon.TimeOfDay)
- datepicker is a writable scalar field; minDate and maxDate are rechecked on save
- columns.yaml accepts type: date and type: time; Scanner/Valuer structs are columns, not relations
- conformance fixture carries date and datetime fields; README, forms and lists docs

admin/openapi/admin.json

@@ -615,6 +615,9 @@
                     "default": {
                         "$ref": "#/components/schemas/cabana.jsonScalar"
                     },
+                    "displayFormat": {
+                        "type": "string"
+                    },
                     "emptyOption": {
                         "type": "string"
                     },
@@ -632,6 +635,18 @@
                         },
                         "type": "array"
                     },
+                    "firstDay": {
+                        "description": "FirstDay is the first day of the week, 0 (Sunday) to 6.",
+                        "type": "integer"
+                    },
+                    "format": {
+                        "description": "Format is a datepicker's WinterCMS (PHP date) display format;\nDisplayFormat is the same format in the SPA's moment-style tokens.",
+                        "type": "string"
+                    },
+                    "ignoreTimezone": {
+                        "description": "IgnoreTimezone keeps a datetime's wall-clock value with no conversion.",
+                        "type": "boolean"
+                    },
                     "imageHeight": {
                         "type": "integer"
                     },
@@ -642,6 +657,9 @@
                     "label": {
                         "type": "string"
                     },
+                    "maxDate": {
+                        "type": "string"
+                    },
                     "maxFiles": {
                         "description": "MaxFiles caps the number of files of an attachMany field.",
                         "type": "integer"
@@ -657,8 +675,12 @@
                         },
                         "type": "array"
                     },
+                    "minDate": {
+                        "description": "MinDate and MaxDate bound a datepicker's calendar date (YYYY-MM-DD),\nchecked again on save.",
+                        "type": "string"
+                    },
                     "mode": {
-                        "description": "Mode is the fileupload mode (image or file, default file).",
+                        "description": "Mode is the fileupload mode (image or file, default file) or the\ndatepicker mode (date, datetime or time, default datetime).",
                         "type": "string"
                     },
                     "multiple": {
@@ -714,6 +736,10 @@
                         ],
                         "description": "ThumbOptions carries the preview thumbnail mode."
                     },
+                    "twelveHour": {
+                        "description": "TwelveHour shows a 12-hour clock.",
+                        "type": "boolean"
+                    },
                     "type": {
                         "type": "string"
                     },
@@ -724,6 +750,13 @@
                     "widget": {
                         "description": "Widget is the custom-element tag of a `type: widget` field (D-06).",
                         "type": "string"
+                    },
+                    "yearRange": {
+                        "description": "YearRange is [n] (years either side of today) or [from, to].",
+                        "items": {
+                            "type": "integer"
+                        },
+                        "type": "array"
                     }
                 },
                 "required": [