Show a colour-coded team picker instead of cycling with T

T used to silently cycle Model.activeTeamID through the caller's teams with
no visible list of choices. It now opens a full picker (modelled on the
existing user picker) listing every team plus "All teams", each with a
stable identity colour from a new six-colour theme palette. The same colour
now also shows as a bullet next to "team: <name>" in the header, so the
active team stays visible without opening the picker.

Adds an Identity palette to the theme package (six hues, skipping the ones
that already mean firing/critical), Styles.TeamColor to pick one by team id,
and identity_1..6 as theme-file tokens alongside the existing twelve so a
fully custom theme can still set every token.

internal/tui/styles_test.go

@@ -66,6 +66,36 @@ func TestStyles_EachBuiltinIsFullyPopulated(t *testing.T) {
 				t.Errorf("%s: %s has no foreground", th.Name, what)
 			}
 		}
+		for i := range th.Identity {
+			if s.TeamColor(int64(i)).GetForeground() == (lipgloss.NoColor{}) {
+				t.Errorf("%s: identity %d has no foreground", th.Name, i)
+			}
+		}
+	}
+}
+
+// TestStyles_TeamColorIsStableAndDistinct checks the property the header badge
+// and the team picker both rely on: the same id always reads the same colour,
+// and ids that differ (up to the size of the palette) read as different
+// colours rather than all collapsing to one.
+func TestStyles_TeamColorIsStableAndDistinct(t *testing.T) {
+	s := newStyles(theme.GruvboxDark)
+
+	seen := make(map[lipgloss.Color]bool)
+	for id := int64(0); id < 6; id++ {
+		seen[s.TeamColor(id).GetForeground().(lipgloss.Color)] = true
+	}
+	if len(seen) != 6 {
+		t.Errorf("expected 6 distinct colours across 6 ids, got %d", len(seen))
+	}
+
+	// ids repeat past the palette size, and a negative id (never sent by the
+	// server, but cheap to guard) must not panic.
+	if s.TeamColor(6).GetForeground() != s.TeamColor(0).GetForeground() {
+		t.Error("the palette should wrap rather than index out of range")
+	}
+	if got := s.TeamColor(-1).GetForeground(); got == (lipgloss.NoColor{}) {
+		t.Error("a negative id should still resolve to a colour, not panic or fall back to none")
 	}
 }