Let each workflow watch the due date or the start date

Deck 1.18 added a start date to cards (Card::$startdate), so a workflow
no longer has to mean "overdue". Each rule now carries a date_field
('due' | 'start'), chosen in the settings form next to board and stacks.

Existing rules keep the due date: the new column's default supplies it
for every stored row, so there is no backfill step, and
Workflow::getDateFieldOrDue() covers entities that were never near the
database as well as hand-edited values. The controller is the one place
that rejects an unknown value instead of normalising it - a client
asking for a rule it would not get should hear about it.

The probe for the field is property_exists(), not method_exists():
Deck's entities declare no getter as real code - getStartdate(),
getDuedate(), even getId() all go through Entity::__call(), which
method_exists() ignores by definition. A method_exists() guard would
have been false on every Deck version and would have turned every
start-date rule into a silent no-op.

assertDeckAvailable() now also refuses Deck older than 1.18.0. That
floor cannot live in appinfo/info.xml - neither the server's nor the app
store's schema has an app-to-app dependency element - but
<nextcloud min-version="34"> already implies it, since 1.18.x is the
only Deck release line published for Nextcloud 34.

isOverdue() becomes hasPassed(): one function for both dates, since the
comparison and the argument against Deck's day-truncating
getDaysUntilDue() are identical for either.

Also carries a pending NcSelect icon-alignment fix that was already in
the working tree.

Bump to 34.1.0.

lib/Db/Workflow.php

@@ -22,6 +22,8 @@ use OCP\DB\Types;
  * @method void setFilterUserIds(?string $filterUserIds)
  * @method string|null getFilterLabelIds()
  * @method void setFilterLabelIds(?string $filterLabelIds)
+ * @method string|null getDateField()
+ * @method void setDateField(string $dateField)
  * @method bool getNotifyEmail()
  * @method void setNotifyEmail(bool $notifyEmail)
  * @method bool getEnabled()
@@ -30,6 +32,14 @@ use OCP\DB\Types;
  * @method void setLastRun(?\DateTime $lastRun)
  */
 class Workflow extends Entity implements \JsonSerializable {
+	/** Deck's `Card::$duedate` — the card is picked up once it is overdue. */
+	public const DATE_FIELD_DUE = 'due';
+
+	/** Deck's `Card::$startdate` — the card is picked up once its start date has been reached. */
+	public const DATE_FIELD_START = 'start';
+
+	public const DATE_FIELDS = [self::DATE_FIELD_DUE, self::DATE_FIELD_START];
+
 	protected $userId;
 	protected $title;
 	protected $boardId;
@@ -37,6 +47,7 @@ class Workflow extends Entity implements \JsonSerializable {
 	protected $targetStackId;
 	protected $filterUserIds;
 	protected $filterLabelIds;
+	protected $dateField;
 	protected $notifyEmail;
 	protected $enabled;
 	protected $lastRun;
@@ -50,11 +61,29 @@ class Workflow extends Entity implements \JsonSerializable {
 		$this->addType('targetStackId', Types::INTEGER);
 		$this->addType('filterUserIds', Types::STRING);
 		$this->addType('filterLabelIds', Types::STRING);
+		$this->addType('dateField', Types::STRING);
 		$this->addType('notifyEmail', Types::BOOLEAN);
 		$this->addType('enabled', Types::BOOLEAN);
 		$this->addType('lastRun', Types::DATETIME);
 	}
 
+	/**
+	 * The date field to evaluate, never anything else.
+	 *
+	 * Rows written before the column existed carry 'due' from the schema
+	 * default, but a freshly constructed entity holds `null` and a hand-edited
+	 * row could hold anything. Falling back to the due date keeps the old
+	 * behaviour for every value that is not explicitly the start date — the
+	 * safe direction, since 'due' is what every workflow meant before this
+	 * choice existed.
+	 *
+	 * @return self::DATE_FIELD_*
+	 */
+	public function getDateFieldOrDue(): string {
+		$field = $this->getDateField();
+		return in_array($field, self::DATE_FIELDS, true) ? $field : self::DATE_FIELD_DUE;
+	}
+
 	/**
 	 * @return string[]
 	 */
@@ -90,6 +119,7 @@ class Workflow extends Entity implements \JsonSerializable {
 			'targetStackId' => $this->getTargetStackId(),
 			'filterUserIds' => $this->getFilterUserIdsArray(),
 			'filterLabelIds' => $this->getFilterLabelIdsArray(),
+			'dateField' => $this->getDateFieldOrDue(),
 			'notifyEmail' => (bool)$this->getNotifyEmail(),
 			'enabled' => (bool)$this->getEnabled(),
 			'lastRun' => $this->getLastRun()?->format(\DateTimeInterface::ATOM),