feat(tasks): write a task straight into a section

The box at the top puts things in the project with no section, which is right for
capturing. But a project has sections because the work belongs somewhere, and
dragging every new task down into the right one is a second gesture for something
you already knew when you typed it.

Two ways in, because they answer different moments. A field at the foot of each
section and each board column — standing there is enough, no syntax to know. And
`/section` in quick add, for the box at the top and for Today and Upcoming, where
you are not standing in a section at all.

The field goes through quick add rather than createTask, so a line written there
still parses its dates, priorities and labels.

The sigil needed care: '#' and '@' never turn up in a Danish task line by accident
and '/' turns up constantly. It has to follow whitespace and be followed
immediately by the name, which "km/t", "3/4" and "20 kr / stk" all fail. The bare
form is greedy, because "Kunder/Ordrer" is a real section name and the sigil is
inside it.

A section id from the client is checked against the project the task actually
landed in. A `#project` in the same line can move the task elsewhere, and the id
would otherwise follow it into a project that section does not belong to.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/src/lib/api.js

@@ -267,7 +267,8 @@ export const api = {
 	reopenTask: (id) => post(`/tasks/${id}/reopen`),
 	moveTask: (id, data) => post(`/tasks/${id}/move`, data),
 
-	quickAdd: (text, projectId) => post('/tasks/quick-add', { text, project_id: projectId }),
+	quickAdd: (text, projectId, sectionId) =>
+		post('/tasks/quick-add', { text, project_id: projectId, section_id: sectionId }),
 	quickAddPreview: (text, signal) =>
 		get(`/tasks/quick-add/preview?text=${encodeURIComponent(text)}`, { signal }),