Fix unusable personal settings form: v8 Vue idioms and Deck relations

The settings page rendered, but nothing in it worked:

- All NcSelect dropdowns showed "undefined" for every option. In
  @nextcloud/vue 9 the `label` prop is vue-select's option display *key*,
  not a caption, so `label="Board"` read `option.Board`. Use `input-label`.
- Saving always failed with "Bitte einen Titel angeben". Vue 3 dropped
  `.sync`; NcTextField and NcCheckboxRadioSwitch bind via `modelValue`, so
  `:value.sync` / `:checked.sync` never wrote back. Use `v-model`.
- NcButton's style prop is now `variant`, `type` is the native button type
  and `native-type` is gone. `type="tertiary"` rendered
  `<button type="tertiary">`, which HTML falls back to `submit` for, making
  the cancel button submit the form.
- The user dropdown was always empty. Deck's RelationalEntity replaces
  resolved relations with a RelationalObject once an entity is enriched, so
  `$acl->getParticipant()` returns that wrapper and the uid lives in
  `getPrimaryKey()` -- probing for `getUID()` yielded null. This also broke
  the background job's assigned-user filter, which shares the extractor.
- A board's ACL never contains its owner (a private board has an empty
  ACL), so participants are now seeded with the owner, group ACL entries
  are expanded via IGroupManager and display names resolved via
  IUserManager.
- One board appeared twice: getUserBoards() merges own/group/circle boards
  and includes archived and trashed ones. Deduplicate by id and drop those.

Also keep one failing lookup in onBoardChange from taking the other two
dropdowns down with it, and document all of the above in CLAUDE.md.

CLAUDE.md

@@ -90,6 +90,22 @@ None of these were discoverable locally — there's no npm here (see "Local-only
 - **`createAppConfig` prefixes every entry name with the app id**, so the entry `personal-settings` is emitted as `js/workflow_deck_automation-personal-settings.mjs` and `css/workflow_deck_automation-personal-settings.css`. `Util::addScript()`/`addStyle()` take that *full on-disk basename* (minus extension), not the bare entry name — `lib/Settings/Personal.php` therefore passes `Application::APP_ID . '-personal-settings'`. Getting this wrong produces a **silently blank settings page**: the template's empty mount `<div>` renders fine, and the only symptom is `Could not find resource workflow_deck_automation/js/….js to load` (`jsresourceloader`) plus a matching `Could not find resource file "/apps/workflow_deck_automation/css/….css"` in `nextcloud.log`. If you rename the entry in `vite.config.js`, rename it in `Personal.php` too.
 - **The bulk of the CSS lives in a hashed `*.chunk.css`**, loaded at runtime by the `.mjs` bundle (`cssCodeSplit: true`). The `css/workflow_deck_automation-personal-settings.css` that `addStyle()` points at is the ~100-byte stub produced by `createEmptyCSSEntryPoints: true`. A near-empty entry CSS file is expected — don't "fix" it by turning off code splitting.
 
+## `@nextcloud/vue` 9 component API (Vue 3) — the v8 idioms silently do nothing
+
+This app is on `@nextcloud/vue` ^9 / Vue 3. The v8 (Vue 2) prop spellings that most Nextcloud app code online still uses either fail silently or, worse, land as stray DOM attributes instead of erroring:
+
+- **No `.sync`.** Vue 3 removed it. `NcTextField` and `NcCheckboxRadioSwitch` both bind through `modelValue`/`update:modelValue`, so it's `v-model="x"` — `:value.sync="x"` / `:checked.sync="x"` leave the bound state permanently at its initial value. That's how `form.title` stayed `''` and every save died on "Bitte einen Titel angeben."
+- **`NcSelect`'s `label` prop is the *option display key*, not a caption** (it's vue-select's). Passing `label="Board"` makes it read `option.Board` on every option and render `undefined` for all of them. The visible caption prop is `input-label`.
+- **`NcButton`: `variant` is the style, `type` is the native button type**, and `native-type` no longer exists (v8's `type="primary"` + `native-type="submit"` → v9's `variant="primary"` + `type="submit"`). A leftover `type="primary"` renders `<button type="primary">`, which HTML treats as the invalid-value default `submit` — so a *cancel* button silently submits the form.
+- `NcSelect`'s `reduce` is not declared on `NcSelect` itself; it reaches vue-select through attribute fallthrough (NcSelect's root element *is* the `VueSelect` component and it doesn't set `inheritAttrs: false`). It works, but it's fallthrough, not a documented prop.
+- `NcNoteCard`'s prop is still `type` (`success|info|warning|error`) — not everything was renamed to `variant`.
+
+## Deck entities are "relational": getters don't return the uid string
+
+Deck's `RelationalEntity` swaps resolved relations for an `OCA\Deck\Db\RelationalObject` once an entity is enriched. So on an enriched board/card, `$acl->getParticipant()`, `$board->getOwner()` and a card assignment's participant return a `RelationalObject` (wrapping `OCA\Deck\Db\User`/`Group`/`Circle`), **not** a uid — the uid is its `getPrimaryKey()`. Probing for `getUID()` on the returned object finds nothing and yields `null`, which is how the settings UI's user dropdown came up empty *and* why the runner's assigned-user filter could never match. `DeckIntegrationService::unwrapUid()` handles both shapes (bare string and `RelationalObject`); route any new participant/owner field through it.
+
+Two more Deck facts that bit us in the same pass: a board's ACL does **not** contain its owner (a private board has an empty ACL, so participants must be seeded with `$board->getOwner()`), and ACL entries can be groups (`type === 1`) whose members have to be expanded via `IGroupManager`. `BoardService::getUserBoards()` merges own/group/circle boards and can return the same board twice, and it includes archived and trashed boards — `listBoardsForCurrentUser()` dedupes by id and drops those.
+
 ## Local-only notes
 
 `CLAUDE.local.md` (gitignored) carries session-specific environment notes (e.g. "no PHP/npm available locally"). Check it at the start of work in this repo — it's not duplicated here since it can change independently of the committed guidance.