Playtest #4 fixes: tile picking, knocked-down state, element gauges, draft timer, live stats, shop items, drones, 赫默, 炎佑, UI flash

- #1 picking by the tile under the pointer (prep, battle, pen, equipment drops); the dragged model stays
  under the pointer (mouse and touch); pixel probe removed; phone ghost-click on the underframe fixed
- #2 two-tap confirm on 机变 cards (like the shop)
- #3 a 同盟 room with one human is untimed like 独立模拟 (no countdown outside battles)
- #4 strategy draft: one synced countdown, 30 s per human turn, timeout takes the highlighted band
- #5 special 维式重锤 (4) and 突变细胞 no longer sold; item card shows where they come from
- #6 operator skill-mode sounds no longer play on normal attacks (纯烬艾雅法拉 and 55 others)
- #7 detail card shows live battle stats and the prep-time battle-start stats (g.unitStats)
- #8 official element gauges on units; burst cooldown (阻回) per PRTS
- #9 knocked-down operators stay on their tile with a redeploy countdown ring
- #10 drone behaviour per PRTS (暴鸰, 先兆者 shells, 黑云, 萨科塔之眼)
- #11 赫默's drone only from her skill; placeable summons limited to talent tokens
- #12 炎佑 stays where it is with no enemies; 祛恶之焰 as a continuous channel
- #13 the occasional giant bond icon (loading texture scaled ×46) fixed
- docs (DESIGN §18), recordings, data and tests updated (2467 unit tests, all browser suites green)

test/render/browser.test.js

@@ -164,8 +164,9 @@ describe('render engine in headless Chrome', { skip }, () => {
     const placed = await page.evaluate((uid) => window.__demo.scene.state.board.find((p) => p.uid === uid) || null, info.uid);
     assert.ok(placed, 'piece moved to the board');
     assert.deepEqual([placed.row, placed.col], [10, 5]);
-    const r2 = await page.evaluate(() => window.__demo.view.pieceScreenRect(window.__demo.scene.state.board[1].uid));
-    await page.mouse.click(r2.left + r2.width / 2, r2.top + r2.height / 2, { button: 'right' });
+    // picking is by tile (user playtest #4 item 1): right-click the unit's own tile
+    const r2 = await page.evaluate(() => { const p = window.__demo.scene.state.board[1]; return window.__demo.view.tileScreen(p.row, p.col); });
+    await page.mouse.click(r2.x, r2.y, { button: 'right' });
     await wait(150);
     const log = await page.evaluate(() => window.__demo.log.join('\n'));
     assert.match(log, /pieceClick .*"detail":true/);