fix(app): windowResizability(.contentMinSize) so window stops auto-resizing

Root cause of the "window grows whenever I switch to Chat / the
v2.3 Sessions tab" bug. Prior commits (4baa3d4 sessions-tab
clamp, 9aad905 chat+projects detail-area clamp) were defensive
but not sufficient — with the actual window policy treating
content's ideal height as a BINDING (not a minimum), those
clamps only kept things inside the view, not inside the window.

scarfApp's WindowGroup had .defaultSize(width: 1100, height: 700)
but no explicit .windowResizability(...) modifier. On macOS, a
non-Settings WindowGroup defaults to .automatic, which evaluates
to .contentSize — meaning every layout pass rebinds the window to
the currently-displayed detail view's ideal height. Explains
every symptom:

- Switching to Chat / Sessions grows the window to content size
- User drag-to-resize snaps back on next layout
- Sections with ScrollView-bounded content (Dashboard, Insights)
  "work" because their ideal height is their visible slot
- Resize while in a bounded section looks sticky because the
  rebind target doesn't push back
- Coming back to Chat reasserts the bind and the window grows
  again — sometimes past the screen

Switched to .windowResizability(.contentMinSize). Content's ideal
height is now a minimum FLOOR — user resize works freely, the
window persists across section switches, and it still can't
shrink below a section's minimum render (so tool bars, input
fields, etc. stay visible).

Pre-existing pre-v2.3 bug; v2.3's new content-heavy surfaces
(per-project Sessions list) just made it much more obvious. The
earlier clamp commits stay in — they're still correct for
intra-view layout, just not the window-level fix.

80/80 Swift tests still pass. No test change; behavior is
platform-layout-policy level.

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

scarf/scarf/scarfApp.swift

@@ -86,6 +86,19 @@ struct ScarfApp: App {
             registry.defaultServerID
         }
         .defaultSize(width: 1100, height: 700)
+        // Without an explicit resizability, `WindowGroup` defaults to
+        // `.automatic` which on macOS evaluates to `.contentSize` —
+        // meaning the window is BOUND to its content's ideal size
+        // rather than bounded-below by it. Any section whose content's
+        // intrinsic height changes (Chat's message list, the v2.3
+        // per-project Sessions tab, Insights charts) would resize the
+        // window on every section switch, snap back against user
+        // resize, and sometimes push the whole window past the
+        // screen. `.contentMinSize` turns the content's ideal height
+        // into a minimum floor: user resize works freely, the window
+        // stays put across section switches, and it still can't shrink
+        // smaller than a section's minimum render.
+        .windowResizability(.contentMinSize)
         .commands {
             CommandGroup(after: .appInfo) {
                 Button("Check for Updates…") { updater.checkForUpdates() }