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/theme/load.go

@@ -32,6 +32,13 @@ type rawTheme struct {
 	SevError    *string `yaml:"sev_error"`
 	SevWarning  *string `yaml:"sev_warning"`
 	SevInfo     *string `yaml:"sev_info"`
+
+	Identity1 *string `yaml:"identity_1"`
+	Identity2 *string `yaml:"identity_2"`
+	Identity3 *string `yaml:"identity_3"`
+	Identity4 *string `yaml:"identity_4"`
+	Identity5 *string `yaml:"identity_5"`
+	Identity6 *string `yaml:"identity_6"`
 }
 
 // binding ties a YAML key to its raw value and the field it fills, so parsing,
@@ -56,6 +63,12 @@ func bindings(r *rawTheme, t *Theme) []binding {
 		{"sev_error", r.SevError, &t.SevError},
 		{"sev_warning", r.SevWarning, &t.SevWarning},
 		{"sev_info", r.SevInfo, &t.SevInfo},
+		{"identity_1", r.Identity1, &t.Identity[0]},
+		{"identity_2", r.Identity2, &t.Identity[1]},
+		{"identity_3", r.Identity3, &t.Identity[2]},
+		{"identity_4", r.Identity4, &t.Identity[3]},
+		{"identity_5", r.Identity5, &t.Identity[4]},
+		{"identity_6", r.Identity6, &t.Identity[5]},
 	}
 }