docs: mark Phase 1.5 done; sync architecture, modernize, readme

- ROADMAP: all Phase 1.5 boxes checked; done-notes (clone snapshots,
  Copy handle, no Instant on wasm, button enables with the pending burst)
- ARCHITECTURE: undo/redo in the header tree and a paragraph on the
  snapshot history; gaps list no longer mentions undo
- README: undo/redo in 'What works today'

ARCHITECTURE.md

@@ -100,8 +100,8 @@ JSON as-is.
 ## Component tree
 
 App
-├─ Header         name, image, date steppers, session steppers,
-│                 Save (download)/Load (file import)/Clear (wipe)
+│                 Save (download)/Load (file import)/Clear (wipe),
+│                 ↩ Undo/redo (buttons + Ctrl+Z / Ctrl+Shift+Z / Ctrl+Y)
 ├─ Modal          overlay dialog: confirm (action) or error (close)
 ├─ Sidebar
 │  ├─ Image       portrait
@@ -133,6 +133,13 @@ then a debounced (500 ms) effect writes on any store change via
 `Settings::VERSION` (the migration hook). `ModalState` holds title/message/
 action as signals; the confirm button reads the action at click time.
 
+Undo/redo lives in `state::undo`: the same store trigger feeds a
+snapshot history (`HistoryHandle` in context). The first change of a
+burst is remembered; when the burst goes quiet for 1 s, the pre-burst
+state becomes an undo step. Undo/redo restore via `replace_state` —
+the autosave effect persists the undone state too. Clear and import
+push a snapshot first, so they are undoable themselves.
+
 `Numput` is the shared numeric input: `+n`/`-n` adjust relative to the
 current value, a plain number sets absolutely, invalid input is reverted,
 and the value renders with thousands separators. `NumputChange` is the same
@@ -157,8 +164,6 @@ currently mounted on any page.
 ## Current gaps
 
 - Quests, notes, contacts: models and mock data only
-- No undo/redo (planned as Phase 1.5; snapshot-based, rides on the
-  persist machinery)
 - `Character` and `Wiki` pages render placeholders
 - Prepared spells list is empty; `Spell` is a name-only stub; attunements
   have no UI; `Settings` has only `version`

README.md

@@ -8,6 +8,8 @@ game. The UI is in Russian.
 - Campaign header: name, in-game date steppers, session counter, and
   Save / Load / Clear: download `dashboard.json`, import a file back,
   wipe to a blank campaign
+- Undo/redo: header buttons and Ctrl+Z / Ctrl+Shift+Z / Ctrl+Y over
+  edit bursts; Clear and import are undoable too
 - Character sidebar: portrait, names, class, level, XP, hit points with
   temp HP bar, hit dice, death saves, spell slots
 - Inventories page (`/inv`): personal and party-common inventories,

ROADMAP.md

@@ -105,21 +105,30 @@ Snapshot-based undo rides on the Phase 1 machinery: serialize → push →
 fires on any mutation, so no component changes are needed and every later
 phase's edits are undoable from day one.
 
-- [ ] `state::undo.rs` (hydrate-gated): undo/redo stacks of serialized
+- [x] `state::undo.rs` (hydrate-gated): undo/redo stacks of serialized
   `Dashboard`, capped (e.g. 100); push coalesced on the store trigger
   (one snapshot per ~1 s window → one undo step = one edit burst)
-- [ ] a new edit after undo clears the redo stack; Clear and import push a
+- [x] a new edit after undo clears the redo stack; Clear and import push a
   snapshot first, so they are undoable too
-- [ ] `undo()` / `redo()` call `replace_state`; expose stack depths as
+- [x] `undo()` / `redo()` call `replace_state`; expose stack depths as
   `RwSignal<usize>` for button disabled states
-- [ ] header buttons: ↩ Отменить / Вернуть (disabled when empty)
-- [ ] shortcuts: Ctrl+Z, Ctrl+Shift+Z (Ctrl+Y); ignore when focus is in an
+- [x] header buttons: ↩ Отменить / Вернуть (disabled when empty)
+- [x] shortcuts: Ctrl+Z, Ctrl+Shift+Z (Ctrl+Y); ignore when focus is in an
   input/textarea/select, so typing never triggers undo
-- [ ] unit tests for stack semantics; e2e: edit → undo → redo; reload keeps
+- [x] unit tests for stack semantics; e2e: edit → undo → redo; reload keeps
   the undone state (undo writes through autosave)
 - **Acceptance:** every edit since the last window is reversible with a
   keystroke; undo survives a reload.
 
+**Done (2026-08-16):** implementation in `src/state/undo.rs`; e2e-verified
+in chromium (buttons, shortcuts, reload, undoable Clear). Notes:
+- Snapshots are `Dashboard` clones, not JSON: the dashboard is small.
+- `HistoryHandle` is `Copy` (RwSignal fields) — context-friendly and
+  capture-safe under edition-2024 closure rules.
+- No `std::time::Instant`: it panics on wasm32; the settle timer is the
+  only clock. The undo button enables with the pending burst, so a
+  fresh edit is undoable before the 1 s window settles.
+
 ## Phase 2 — Character page (M, ~1-2 days)
 
 `/` currently renders the literal string "character".