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

modules/cabana/README.md

@@ -18,6 +18,7 @@ Schema-driven admin backend that compiles WinterCMS-style YAML list, form, filte
 - Controller assets: a controller implementing `pact.AdminClientAssets` names JS (`.js`, `.mjs`) and CSS files under its plugin's `assets/` directory, Winter's `addJs`/`addCss`. They are read from the plugin's embedded tree at boot (a missing file fails boot; there is no disk override) and listed in the list and form schemas under `assets` as same-origin URLs with a `?v=` content hash. A form with a widget needs at least one JS file.
 - Toolbar actions: `toolbar.buttons` in `config_list.yaml` lists the built-in `create` and `delete` next to names the controller registers through `pact.HasAdminActions`. Registered actions share one namespace with widget actions, `create` and `delete` are reserved, and each toolbar action needs a label. The list schema's `toolbarActions` carries only the actions the requesting administrator may run, with localized labels; an unknown name fails boot.
 - Server-rendered partials: `headerPartial: <name>` in `config_list.yaml` (a strip above the list) and `type: partial` with `path: <name>` in `fields.yaml` render the template `{ConfigDir}/_<name>.htm` with `html/template` against a view model from the controller's `pact.AdminPartialData`. The result reaches the SPA as an allowlisted node tree, never as an HTML string. A missing or unparsable template, a free-form path or a controller without `pact.AdminPartialData` fails boot.
+- Date pickers: a `type: datepicker` field in `fields.yaml` edits a date (`mode: date`, a `lagoon.Date` column), a date and time (`mode: datetime`, the default, a `time.Time` column stored in UTC) or a time of day (`mode: time`, a `lagoon.TimeOfDay` column); pointers to the three types make the value optional. It accepts WinterCMS's `mode`, `format` (a PHP `date()` format, served also as `displayFormat` in the SPA's tokens), `minDate`, `maxDate`, `yearRange`, `firstDay`, `twelveHour` and `ignoreTimezone`; any other key, a format letter with no equivalent, bounds on `mode: time`, `ignoreTimezone` outside `mode: datetime` or a column whose Go type does not match the mode fails boot. The save rechecks `minDate` and `maxDate` on the calendar date and answers 422 on the field. List columns take `type: date` and `type: time` for these columns, and a struct column that implements `sql.Scanner` or `driver.Valuer` is never taken for a relation.
 - File uploads: a `type: fileupload` field in `fields.yaml` edits an attachOne or attachMany relation the record model declares through `attach.HasRelations` (its `AttachRelations` method) next to `attach.Owner`. The field accepts WinterCMS's `mode` (`image` or `file`), `fileTypes`, `mimeTypes`, `maxFilesize` (megabytes), `maxFiles` (attachMany only), `imageWidth`, `imageHeight`, `thumbOptions` (only `mode`: `auto`, `exact`, `crop` or `fit`), `useCaption` and `prompt`; any other key, an image-mode file type outside jpg, jpeg, png, gif and webp, a name that is not a declared relation or a `maxFilesize` above `http.body_limits.upload_bytes` fails boot. Uploads and removals are deferred, as in WinterCMS: the SPA sends a random form session key in the `X-Session-Key` header (`cabana.SessionKeyHeader`) with every file call and with the save, the server keeps the pending work in `deferred_bindings` against that key and the signed-in administrator, and the record's next create or update save applies it inside its transaction. A save that fails with 422 keeps the pending uploads; another administrator's key matches nothing. The upload route caps the request body at the smaller of `http.body_limits.upload_bytes` and `maxFilesize` plus 64 KiB and answers 413 `payload_too_large` past it; the size, type and image checks run on the server (through `attach.Store`) and answer 422 on the field. A file list (`cabana.FileItem`) carries `url` and `thumb_url` only for a public relation.
 - Singleton settings screens declared with `pact.HasSettings`, read and saved by `cabana.SettingsService`.
 - Backend navigation (`pact.HasNavigation`) and permissions (`pact.HasPermissions`), filtered per user by `cabana.Registry.Metadata`. An administrator's own `backend_users.permissions` are merged over the role's as in Winter (a `-1` denies a code the role grants). `cabana.Allows` implements the permission check with Winter's `hasAnyAccess` semantics: superusers pass, a principal needs any one of the listed codes, and wildcards match on both sides (a grant ending in `.*` covers every code with that prefix, and a required code ending in `.*` is met by any grant under it).
@@ -194,6 +195,8 @@ func (p *Plugin) AdminFS() fs.FS { return adminFS }
 | `backend.uri` | `/backend` | Admin mount path. One or more lowercase path segments; boot fails on an invalid value. |
 | `backend.cookie_secure` | `true` | Set `false` to drop the cookie's Secure attribute for plain-HTTP development. Refused in the `production` environment. |
 | `app.url` | empty | Base URL used for the token issuer. |
+| `http.body_limits.upload_bytes` | none | Read from the HTTP configuration: caps the body of a file upload (together with the field's `maxFilesize` plus 64 KiB), and no fileupload field may declare a larger `maxFilesize`. Without it the cap is the field's limit, or 128 MiB. |
+| `http.body_limits.default_bytes` | none | Read from the HTTP configuration: caps the JSON bodies of the file caption and reorder routes (1 MiB when not set). |
 
 The backend user, role and token blacklist tables (`backend_users`, `backend_user_roles`, `backend_jwt_blacklist`) are created by `lagoon.BackendAdminMigrations`, which the `migrate` command runs.