Implement Bastion-owned workspaces (SW_MINIMIZE hide/show, workspace-switch journal ordering)

## Problem / goal

Implement Bastion-owned workspaces: `SW_MINIMIZE`-based hide/show for outgoing/incoming window sets, with proper write-ahead journal ordering for a full workspace switch (not just the single-window hide/restore the v0.1 journal issue covers).

## References

- `DESIGN.md` §4 (Workspace Model in full) — why `SW_MINIMIZE` wins over cloaking/`SW_HIDE`/off-screen parking; the exact switch sequence: write-ahead journal -> minimize outgoing set -> per-window `SetWindowPlacement` into tile -> one Defer batch.
- `DESIGN.md` §3.7 (Workspace Manager).
- Depends on the v0.1 write-ahead-journal issue (extends its schema to multi-workspace) and the Placement Executor issue (`SetWindowPlacement`-into-tile reuse).

## Acceptance criteria

- [ ] Switching workspaces minimizes the outgoing window set via `ShowWindowAsync(SW_MINIMIZE)` by default, with per-rule `SW_HIDE`/`ITaskbarList` curation as an opt-in.
- [ ] The v0.1 journal schema is extended (not replaced) to record window -> workspace assignment, still written before any hide call.
- [ ] Incoming windows restore directly into their tile via `SetWindowPlacement` (reusing the Executor's coordinate-space conversion), landing with no flash at stale geometry.
- [ ] `bastion restore-windows` (v0.1) continues to work correctly against the multi-workspace journal schema.
- [ ] Bastion maintains an independent, persistent layout tree per (native-desktop GUID x monitor) per DESIGN.md §4 — this issue covers native-desktop coexistence (never cloaking foreign windows, never depending on the specific cloak reason flag), not the full per-desktop-partition mechanism (that's its own v0.4 issue) — a single native desktop's worth of Bastion-owned workspaces is in scope here.

Start with DESIGN.md §4 and §3.7 to understand the workspace model, switch sequence, and Workspace Manager. Then inspect the dependent v0.1 write-ahead-journal issue and Placement Executor issue, since this work extends the journal schema and reuses coordinate conversion. Done means multi-workspace switching meets every acceptance criterion, including restore-windows compatibility and native-desktop coexistence.

Written by the indexing model from the issue text.