burger sub-btns: opacity-0.6 inactive default + 2-pulse --priRd flash w. fa-ban swap on click — TDD

Adds the active/inactive distinction to the 5 burger fan sub-btns. Default state is INACTIVE (opacity 0.6, real icon visible); active conditions get wired one-by-one in later sprints as each surface matures.

## Markup (templates/apps/gameboard/_partials/_burger.html)

Each sub-btn now renders BOTH icons:
- `<i class="fa-solid fa-<real> burger-fan-icon--on">` (sky/earth/sea/voice/text)
- `<i class="fa-solid fa-ban burger-fan-icon--off">`

CSS keeps the real icon visible by default in both .active + inactive states. The fa-ban only surfaces during the .flash-inactive pulse below (icon swap is tied to the pulse class, not to inactive state per se — user-spec'd).

## SCSS (static_src/scss/_burger.scss)

- `#id_burger_btn.active ~ ... .burger-fan-btn.active { opacity: 1 }` — active sub-btn fully visible.
- `#id_burger_btn.active ~ ... .burger-fan-btn:not(.active) { opacity: 0.6 }` — inactive default.
- `.burger-fan-icon--on / --off` stacked absolute-position so the swap doesn't shift the layout box.
- `.burger-fan-btn.flash-inactive` — adds --priRd border + glow (box-shadow modeled on sig-select's SAVE SIG countdown but lighter), AND swaps to fa-ban via `.burger-fan-icon--on { display: none } / --off { display: inline-block }`.

The `#id_burger_btn` itself (the trigger btn) is explicitly NOT subject to inactive/active opacity treatment — only the sub-btns.

## JS (apps/epic/static/apps/epic/burger-btn.js)

Delegated click handler on `#id_burger_fan`: any `.burger-fan-btn` click that DOESN'T carry `.active` runs `_flashInactive(subBtn)` — 2 pulses, 180ms ON / 120ms OFF (tighter than sig-select's 600ms cadence per user spec). Active sub-btns will route to their per-feature handlers in later sprints; for now they no-op.

## Tests

- `apps/epic/tests/integrated/test_views.py::RoomBurgerBtnRenderTest::test_each_sub_btn_renders_dual_icon_for_inactive_flash_swap` — asserts `burger-fan-icon--on` + `--off` appear 5 times each (one per sub-btn). fa-ban itself isn't counted directly — `_table_positions.html` also renders fa-ban for non-starter seats — but the burger-fan-icon classes are unique to the fan.
- `static_src/tests/BurgerSpec.js` — 5 new specs under `describe("inactive sub-btn flash")`:
  - adds .flash-inactive on click
  - removes after ~180ms (first ON window)
  - re-adds after ~480ms (second ON window during the 2nd pulse)
  - settles back to default after ~800ms (full 2-pulse cycle)
  - does NOT flash when sub-btn carries .active

Uses `jasmine.clock()` for deterministic timing. Mirror-copied to `static/tests/BurgerSpec.js` for the Jasmine FT runner.

## Verification

1358 IT+UT green. Jasmine FT runs all specs (incl. the 5 new flash specs) green.

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Sonnet 4.6 <noreply@anthropic.com>

src/static/tests/BurgerSpec.js

@@ -196,6 +196,51 @@ describe("Burger", () => {
         });
     });
 
+    describe("inactive sub-btn flash", () => {
+        let subBtn;
+
+        beforeEach(() => {
+            subBtn = document.createElement("button");
+            subBtn.className = "burger-fan-btn";
+            fan.appendChild(subBtn);
+            jasmine.clock().install();
+        });
+
+        afterEach(() => {
+            jasmine.clock().uninstall();
+        });
+
+        it("adds .flash-inactive to inactive sub-btn on click", () => {
+            subBtn.click();
+            expect(subBtn.classList.contains("flash-inactive")).toBe(true);
+        });
+
+        it("removes .flash-inactive after the ON window (~180ms)", () => {
+            subBtn.click();
+            jasmine.clock().tick(200);
+            expect(subBtn.classList.contains("flash-inactive")).toBe(false);
+        });
+
+        it("pulses twice — second ON window arrives after off+on cycle (~480ms)", () => {
+            subBtn.click();
+            // First pulse cycle: 180ms ON + 120ms OFF = 300ms. Second pulse ON starts.
+            jasmine.clock().tick(310);
+            expect(subBtn.classList.contains("flash-inactive")).toBe(true);
+        });
+
+        it("settles back to default after 2 pulses (~700ms total)", () => {
+            subBtn.click();
+            jasmine.clock().tick(800);
+            expect(subBtn.classList.contains("flash-inactive")).toBe(false);
+        });
+
+        it("does NOT flash when sub-btn carries .active class", () => {
+            subBtn.classList.add("active");
+            subBtn.click();
+            expect(subBtn.classList.contains("flash-inactive")).toBe(false);
+        });
+    });
+
     describe("AbortController teardown", () => {
         it("detaches click handler when ac.abort() is called", () => {
             ac.abort();