fix(brainbar): scope results overlay to Dashboard + dismiss on tab-switch + wire click-outside

Closes 3 new P0s from the post-03d66b8a live test:

1. **Click-outside didn't dismiss** — root cause: commit 03d66b8 added
   the `isSearchOverlayDismissed` @published flag to `QuickCaptureViewModel`
   but `BrainBarCommandBarResultsOverlayGate.shouldShow` never actually
   read it. The flag was being set but shouldShow returned true anyway,
   so the overlay stayed visible. The earlier
   `.onTapGesture { viewModel.dismissSearchOverlay() }` on the tab-content
   Group was firing correctly — the dismissed flag just wasn't gating
   anything. Now `shouldShow` checks
   `!isSearchOverlayDismissed` and the overlay hides.

2. **Results overlay persisted across tab switches** — the overlay was
   attached to the Group that swaps dashboard/injections/graph content,
   so it floated above whichever tab was active. Fix: the overlay now
   takes an `isOnActiveTab: Bool` prop; `BrainBarWindowRootView` passes
   `selectedTab == .dashboard`. `shouldShow` short-circuits false when
   off-tab. Belt-and-suspenders: `.onChange(of: selectedTab)` on the
   root view explicitly calls `dismissSearchOverlay()` when the user
   leaves Dashboard, so any future re-architecture of the overlay host
   still clears stale state.

3. **Tap-catcher is now built into the overlay itself** as a full-area
   `Color.clear` + `.onTapGesture` UNDER the results card (ZStack),
   instead of an `.onTapGesture` attached to the underlying Group.
   Previously, clicks on dashboard metric cards could be absorbed by
   their `.background(RoundedRectangle(...))` shapes before reaching
   the Group's handler; the new design puts a guaranteed-transparent
   tap layer behind the card so clicks anywhere outside the card
   reach `dismissSearchOverlay()`. The tap-catcher only exists while
   the overlay is visible, so normal tab-content interactions are
   unaffected at rest.

Also migrates the animation definitions from the parent to the gate —
the ZStack's `.animation(value: shouldShow)` is the single trigger,
replacing the parent-level `.animation(value: ...)` chain that had to
guess which @published property was changing.

Suspected root cause for user's "input stuck after tab-switch" report:
the overlay was holding a visible `Color.clear` tap-shape over the
entire tab region even after navigating to Graph/Injections, which
could confuse AppKit's first-responder dispatch when the user clicked
back into the NSTextField. With the overlay now properly scoped to
Dashboard + dismissing on switch, the tap-catcher no longer lingers,
and the NSTextField owns its own hit region in the header cleanly.

Tests
- `swift test --filter BrainBar` → 270 tests, 0 failures (unchanged).
  The existing `testHandleInputChangeClearsOverlayDismissedFlag` and
  `testDismissSearchOverlayHidesResultsWithoutClearingInput` now
  actually exercise a gate that honours the flag.

Visual verification
- `/tmp/brainbar-v5-search-dashboard.png` — typing "brainlayer" on
  Dashboard shows the results dropdown.
- `/tmp/brainbar-v5-click-outside.png` — click below the results card
  dismisses the overlay; "brainlayer" remains in the input so the
  next keystroke re-shows.

Deferred to commit 5 (as planned): async-off-main submitSearch, teal
hysteresis on hero accent, sparkline dot pixel-snap centering. Deferred
to commit 6: expand-in-context detail drawer (Atomic pattern) +
enrichment metrics redesign.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: EtanHey

brain-bar/Sources/BrainBar/BrainBarCommandBar.swift

@@ -295,26 +295,50 @@ private struct CommandBarTrailingHint: View {
 
 struct BrainBarCommandBarResultsOverlay: View {
     let viewModel: QuickCaptureViewModel?
+    /// Command bar is ALWAYS visible in the header, but the results overlay is
+    /// scoped to the Dashboard tab. When the user switches to Injections or
+    /// Graph, the overlay hides so it doesn't float over unrelated content.
+    let isOnActiveTab: Bool
 
     var body: some View {
         if let viewModel {
-            BrainBarCommandBarResultsOverlayGate(viewModel: viewModel)
+            BrainBarCommandBarResultsOverlayGate(
+                viewModel: viewModel,
+                isOnActiveTab: isOnActiveTab
+            )
         }
     }
 }
 
 private struct BrainBarCommandBarResultsOverlayGate: View {
     @ObservedObject var viewModel: QuickCaptureViewModel
+    let isOnActiveTab: Bool
 
     var body: some View {
-        if shouldShow {
-            BrainBarCommandBarResultsOverlayReady(viewModel: viewModel)
-                .transition(.opacity.combined(with: .move(edge: .top)))
+        ZStack(alignment: .top) {
+            if shouldShow {
+                // Full-area transparent tap-catcher UNDER the results card.
+                // Clicks outside the card dismiss the overlay without clearing
+                // the typed query (the dismissed flag resets on next keystroke).
+                Color.clear
+                    .contentShape(Rectangle())
+                    .onTapGesture {
+                        viewModel.dismissSearchOverlay()
+                    }
+                    .frame(maxWidth: .infinity, maxHeight: .infinity)
+
+                BrainBarCommandBarResultsOverlayReady(viewModel: viewModel)
+                    .padding(.horizontal, 20)
+                    .padding(.top, 10)
+                    .transition(.opacity.combined(with: .move(edge: .top)))
+            }
         }
+        .animation(.easeInOut(duration: 0.18), value: shouldShow)
     }
 
     private var shouldShow: Bool {
-        guard viewModel.mode == .search else { return false }
+        guard isOnActiveTab else { return false }
+        guard viewModel.mode == .search, !viewModel.isSearchOverlayDismissed else { return false }
         return !viewModel.inputText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
     }
 }

brain-bar/Sources/BrainBar/BrainBarWindowRootView.swift

@@ -38,19 +38,14 @@ struct BrainBarWindowRootView: View {
                 }
             }
             .frame(maxWidth: .infinity, maxHeight: .infinity)
-            .contentShape(Rectangle())
-            .onTapGesture {
-                // Click-outside-the-overlay: hide results without clearing the query.
-                commandBarViewModel?.dismissSearchOverlay()
-            }
-            .overlay(alignment: .top) {
-                BrainBarCommandBarResultsOverlay(viewModel: commandBarViewModel)
-                    .padding(.horizontal, 20)
-                    .padding(.top, 10)
-                    .animation(.easeInOut(duration: 0.18), value: commandBarViewModel?.results.count)
-                    .animation(.easeInOut(duration: 0.18), value: commandBarViewModel?.mode)
-                    .animation(.easeInOut(duration: 0.18), value: commandBarViewModel?.inputText.isEmpty)
-                    .animation(.easeInOut(duration: 0.18), value: commandBarViewModel?.isSearchOverlayDismissed)
+            .overlay {
+                // Overlay carries its own full-area tap-catcher and only
+                // renders when the user is on the Dashboard tab with a
+                // non-empty search query that hasn't been dismissed.
+                BrainBarCommandBarResultsOverlay(
+                    viewModel: commandBarViewModel,
+                    isOnActiveTab: selectedTab == .dashboard
+                )
             }
         }
         .frame(