refactor(deck): address PR #826 review feedback

- Modernize the new models (DeckCardSummary, DeckCommentSummary,
  StackOverview, BoardOverviewResponse + the loosened unions) to PEP 604
  syntax (list[...] / X | None), per CLAUDE.md.
- Make status="done" exclude archived cards so open/done/archived partition
  the board with no overlap (a done+archived card is reported only as
  "archived"); document the semantics in docstrings and docs/deck.md, add a
  partition unit test.
- deck_get_archived_stacks: pass through label/assigned_to filters (status
  stays archived-only by definition); note the limitation in the docstring.
- Rename _validate_description_max_length → _validate_positive_length (now a
  generic positive-length guard).
- Soften deck_get_board_overview docstring: it views board state and omits
  the ACL/user/label-management fields deck_get_board exposes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/deck.md

@@ -59,7 +59,7 @@ default** and support filtering so you fetch only what you need.
 | Parameter | Default | Effect |
 |-----------|---------|--------|
 | `detail` | `summary` | `summary` returns compact rows (id, title, stackId, labels as titles, assignee UIDs, due/done, counts, a short `descriptionPreview`); `full` returns the complete card objects (the pre-0.92 shape). |
-| `status` | `open` | Filter before serialization: `open` (excludes archived **and** done), `done`, `archived`, or `all`. |
+| `status` | `open` | Filter before serialization: `open`, `done`, `archived`, or `all`. The first three **partition** the board (no overlap) — a card that is both done and archived is reported only under `archived`. |
 | `label` | – | Only cards carrying a label with this exact title. |
 | `assigned_to` | – | Only cards assigned to this user UID. |
 | `description_max_length` | – | In `detail="full"`, truncate each description. |