feat(projects): change a member's role from the member list

An invite sent with the wrong role could not be corrected. The only way
back was to remove the person and invite them again — and removing a member
unassigns every task they were responsible for, so fixing a dropdown cost
somebody their work. This is the other side of "an external user cannot
create tasks": the rule was right, the role was wrong, and there was no way
to say so.

PATCH against a membership that already exists, not the upsert AddMember
does. Somebody who is not a member is not silently made one: that is an
invite, it belongs to the invite flow, and doing it here would let a typo
in a user id add a stranger to a project without anybody being asked.

The owner is refused, with the real reason rather than the true but useless
one. Ownership lives on the project rather than in project_members, so the
plain answer would have been "not a member" — which is correct and tells
nobody anything. Ownership is transferred, not granted, and two owners is a
state with no way to settle a disagreement about who may remove whom.

In the list, the owner's standing is text and everybody else's is a
dropdown. A disabled control would be a thing that exists to say no.

And the roles are finally in Danish. The API's words are `owner`, `editor`
and `viewer`, and they were being printed straight into a Danish page; the
list now uses the same three phrases the invite form beside it already did.

The smoke test drives both browsers, because the interesting part is that
the other one's permissions really change: a viewer is told the project is
read-only and has no quick-add box, the owner promotes them from the list,
and after a reload the box is there and the notice is gone.

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

docs/openapi.yaml

@@ -1211,9 +1211,46 @@ paths:
     parameters:
       - { name: projectID, in: path, required: true, schema: { type: string } }
       - { name: userID, in: path, required: true, schema: { type: string } }
+    patch:
+      tags: [projects]
+      summary: Change what an existing member may do. The project's owner only.
+      description: |
+        Editor or viewer. An UPDATE against a membership that already exists —
+        somebody who is not a member is not silently made one, because that is an
+        invite and belongs to the invite flow.
+
+        Not the owner: ownership is transferred, not granted, and two owners is a
+        state with no way to settle a disagreement about who may remove whom. The
+        owner also has no membership row at all — ownership lives on the project —
+        so this answers 409 with the real reason rather than "not a member".
+
+        Correcting a role used to mean removing the person and inviting them
+        again, which also unassigns every task they were responsible for.
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required: [role]
+              properties:
+                role: { type: string, enum: [editor, viewer] }
+      responses:
+        "204": { description: Changed. }
+        "404": { $ref: "#/components/responses/NotFound" }
+        "409":
+          description: The owner's standing cannot be changed.
+          content:
+            application/json:
+              schema: { $ref: "#/components/schemas/Error" }
+        "422": { $ref: "#/components/responses/Validation" }
     delete:
       tags: [projects]
       summary: Remove somebody from a project. Its owner only.
+      description: |
+        Their tasks are unassigned rather than left pointing at somebody who can
+        no longer see the project — which is why changing a role is a PATCH and
+        not a remove-and-reinvite.
       responses:
         "204": { description: Removed. }
         "404": { $ref: "#/components/responses/NotFound" }