Problem:
Terminal probes sent with `nvim_ui_send()` can reach more than one stdout TTY
UI. Probes with a known TTY UI owner should not accept `TermResponse`s from
unrelated UI channels. 

Solution:
Thread the existing `chan` filter through owned terminal probes. This covers
startup/attach background detection, fallback truecolor detection, and
`vim.tty.query()` forwarding opts to `vim.tty.request()`.

Note: Not every terminal escape path is updated here. I only passed `chan` when
the caller already knows which TTY UI owns the probe. For example, this does
not include:
- (Followup) OSC 52 (system clipboard) detection. It needs to capture the
  `UIEnter` channel. Adding `{ chan = ... }` only to the nested query would be
  half a fix.
- OSC 52 _paste_ is left global because the provider callback does not have
  a UI channel (paste is invoked without a ui channel/tty ui object).

Problem:
- Various `TermRequest` handlers which all do similar things.
- `tty.query` is specific to `XTGETTCAP DCS`, can't be reused for other kinds of terminal queries.

Solution:
Provide `tty.request()`.

Problem:
Similar to clearmatches(), it's always necessary to provide a fallback
that allows the user to do a "global reset" when something goes wrong.

Solution:
vim.img.del(math.huge) clears all images.

Use kitty's d=A command to clear all placements in a single
escape sequence rather than N individual deletes, also freeing stored
image data not referenced by the scrollback buffer.

Problem:
No builtin api to load and display images.

Solution:
Introduce vim.ui.img. Only supports kitty graphics protocol, currently.