feat(engine): MoveRejectedEvent + PausePlugin (Esc)

- New MoveRejectedEvent fires from end_drag when the cursor is over
  a real pile but the placement is illegal. AudioPlugin plays
  card_invalid.wav on it.
- New PausePlugin + PausedResource: Esc toggles a full-window
  overlay and the flag. tick_elapsed_time and advance_time_attack
  skip work while paused. Help cheat sheet updated.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/SESSION_HANDOFF.md

@@ -2,7 +2,7 @@
 
 > Last updated: 2026-04-25
 > Branch: `master` — pushed to https://git.aleshym.co/funman300/Rusty_Solitare.git
-> Test count: **226 passing** (83 core + 54 data + 89 engine), `cargo clippy --workspace -- -D warnings` clean
+> Test count: **228 passing** (83 core + 54 data + 91 engine), `cargo clippy --workspace -- -D warnings` clean
 
 ---
 
@@ -156,19 +156,24 @@ All sub-phases (3A–3F) done. Plugins: `GamePlugin`, `TablePlugin`, `CardPlugin
 ### Phase 7 (part 2) — Synthesized SFX + AudioPlugin ✅ COMPLETE
 
 - New workspace crate `solitaire_assetgen` with bin `gen_sfx`. Synthesizes five 44.1kHz mono 16-bit PCM WAVs from a deterministic LCG noise source + sine/square synths into `assets/audio/`. Run with `cargo run -p solitaire_assetgen --bin gen_sfx`. Output is committed; end users never run the generator.
-- `AudioPlugin` (`solitaire_engine`): embeds the WAVs via `include_bytes!()`, decodes once via `kira::StaticSoundData::from_cursor`, plays on `DrawRequestEvent` (flip), `MoveRequestEvent` (place), `NewGameRequestEvent` (deal), `GameWonEvent` (fanfare). `card_invalid.wav` is loaded but unused — wiring it needs a `MoveRejectedEvent` (no such event today).
+- `AudioPlugin` (`solitaire_engine`): embeds the WAVs via `include_bytes!()`, decodes once via `kira::StaticSoundData::from_cursor`, plays on `DrawRequestEvent` (flip), `MoveRequestEvent` (place), `NewGameRequestEvent` (deal), `GameWonEvent` (fanfare).
 - Backend handle stored as `NonSend` (cpal stream is `!Send` on some platforms). Plugin degrades gracefully if no audio device is available — logs a warning, gameplay continues silently.
 - Single decode unit test (`embedded_wavs_decode_successfully`) keeps the loader and generator in sync.
 
+### Phase 7 (part 3) — MoveRejectedEvent + Pause Menu ✅ COMPLETE
+
+- New `MoveRejectedEvent { from, to, count }`. `end_drag` fires it when the cursor is over a real pile but `can_place_*` rejects the placement. `AudioPlugin` plays `card_invalid.wav` on it.
+- New `PausePlugin` + `PausedResource(bool)`. **Esc** toggles a full-window pause overlay (ZIndex 220) and flips the resource. `tick_elapsed_time` and `advance_time_attack` skip work while paused. Input is deliberately not blocked — pause is a "stop the clock" screen, nothing more.
+- `HelpPlugin` cheat sheet updated to reflect the new Esc behaviour.
+
 ## What Is Next
 
-### Phase 7 (part 3+) — Pause Menu + Polish
+### Phase 7 (part 4+) — Polish
 
-- **Pause menu**: Esc currently logs a placeholder. Likely a small overlay similar to `HelpPlugin` with a `Paused` resource that gates `Time::delta_secs` in `tick_elapsed_time` / `advance_time_attack`.
-- **`MoveRejectedEvent`** (small): emit from `end_drag` when a drop is on a real pile but validation fails, so `card_invalid.wav` finally has something to fire on.
-- **Volume controls**: Settings overlay with `sfx_volume` slider; persist via `solitaire_data::Settings` (already defined). Apply to kira's main-track gain.
+- **Volume controls**: Settings overlay with `sfx_volume` slider; persist via `solitaire_data::Settings`. Apply to kira's main-track gain.
 - **Ambient loop**: optional sixth WAV — needs taste, deferred.
 - **Onboarding**: first-run banner pointing at the **H**/`?` cheat sheet (single-shot via `Settings.first_run_complete`).
+- **Optional**: block input while paused (drag, hotkeys) for stricter pause semantics.
 
 ### Phase 8 — Sync