fix: do not override a forced color profile with a capability report

[s-johri]

What

WithColorProfile documents that it forces a color profile, but the event loop
replaces that profile when the terminal answers a capability request:

case CapabilityMsg:
	switch msg.Content {
	case "RGB", "Tc":
		if *p.profile != colorprofile.TrueColor {

Program keeps no record of where the profile came from, so this code cannot
tell a caller's choice from a detected value. It overwrites both.

Repro

p := tea.NewProgram(model, tea.WithColorProfile(colorprofile.NoTTY))
// Init or Update returns tea.RequestCapability("RGB").
// On a terminal that answers, the profile becomes TrueColor and color returns.

The new test drives the same path with p.Send(CapabilityMsg{Content: "RGB"}).

Fix

Record that the profile came from the option, then skip the upgrade. Detection
is unchanged, and a program that does not use the option behaves as before.

Found while mapping NO_COLOR to NoTTY. It also affects tests that pin a
profile, which the v2 upgrade guide recommends, and applications with their own
"color: off" setting.

Note for the reviewer

ColorProfileMsg is not sent when the profile is forced, because the profile
does not change. Tell me if you prefer to send it anyway.