Add optional embedded terminal and IPython console tabs to the default PyDM GUI

[ruck314]

Description

Adds two optional tabs to the default PyDM GUI, both off by default and
independent of each other. Both are appended after the existing tabs, so no tab
position changes and Debug Tree is still shown on startup.

• Terminal, an interactive local shell, enabled with
  runPyDM(enableTerminal=True) or python -m pyrogue gui --terminal. Job
  control works, so Ctrl-C, Ctrl-Z, fg and jobs behave normally, as do
  full-screen programs such as vim and htop. Color output, 2000 lines of
  scrollback that retains color, and a dark theme.
• IPython, an IPython session with a Rogue client already connected,
  enabled with runPyDM(enableIPython=True) or python -m pyrogue gui --ipython.
  client, root and pr are in scope against the same server the rest of the
  GUI is using, which is the session the Rogue server suggests at startup opened
  rather than typed out. Tab completion on the tree, highlighting, history search
  and %magics all work. Rich output does not, so no inline plotting, because the
  view is a text screen.

Both start their process the first time the tab is displayed, detach into their
own window and reattach without disturbing the running session, and start a fresh
session if the old one exits.

Both run on the machine displaying the GUI, as the user who launched it, not
on the Rogue server. Anyone who can reach the window gets a shell, or arbitrary
Python, with that user's privileges, and PyDM read-only mode restricts neither.
That is why they are opt-in, and the documentation covers the considerations.

Also fixes a VirtualClient bug this work exposed: its link monitor was not a
daemon thread, so a process that connected a client and never called stop()
could not exit. That hangs the one-line client the server banner suggests when it
is used from python -i, and any script that connects and falls off the end.

Adds pyte and ipython as dependencies, declared with the rest of the GUI
stack.

Details

• Emulation. Qt has no terminal widget, so pyte does the VT emulation and
  the result is painted into a QPlainTextEdit. TerminalScreen overrides
  write_process_input, a pyte no-op that cursor position reports reply
  through, and keeps the scrollback rows pyte would otherwise drop.
• Spawn. openpty plus subprocess, since os.forkpty warns in a
  multi-threaded process from Python 3.12 on. start_new_session cannot grant a
  controlling terminal, so the child goes through /bin/sh reopening the pty
  slave inside the new session; without that there is no foreground process group
  and Ctrl-C stops working. A negative-control test pins it.
• Console. IPython on the same pty rather than an embedded qtconsole: no
  new dependency, and it is a TerminalPanel subclass supplying an argv. Started
  as sys.executable -m IPython -i -c so it imports the same pyrogue, with the
  address interpolated only through repr() and its own client in its own
  process. Neither widget is registered for Qt Designer, which instantiates
  eagerly.
• Tree completion. jedi cannot follow the tree's __getattr__ and crashes on
  its nodes, after which IPython offers only the crash text, so Tab looked
  ignored while ordinary objects completed fine. --IPCompleter.use_jedi=False
  falls back to IPython's own dir() based completer; the cost is jedi's type
  inference on ordinary Python.
• Client shutdown. The monitor thread is joined before atexit runs, so only
  a daemon thread or an explicit stop() lets the process exit. That join is why
  exiting the console did not restart it: the child stayed alive, so the pty never
  reported end of file.
• Docker. Quotes the pydm specifier in docker/rogue/Dockerfile. Unquoted,
  >=1.18.0 was a shell redirection and the image installed pydm unpinned.
• Docs. New terminal_tab.rst and ipython_tab.rst, with
  starting_gui.rst, rogue_widgets.rst and new API pages updated.

Testing. 8 new test files collecting 205 tests, 4 extended: controlling
terminal and job control, descriptor and zombie leaks over repeated spawn and
close cycles, key translation, screen and color rendering, detach and reattach,
option plumbing for both tabs, and for the console the Qt-free startup code, a
real session on a pty, tree completion at a real prompt, exiting with a client
attached, and reads and writes against a real server. Full suite: 863 pass, 10
skip, 3 fail. scripts/run_linters.sh clean.

Two failures are pre-existing and unrelated, confirmed with this branch's changes
stashed: test_pydm_rogue_plugin.py calls object.__new__ on a class that
overrides it, which Python 3.14 rejects, and test_epicsV7.py needs softioc,
absent from conda.yml. The third,
test_terminal_takes_focus_when_its_tab_is_selected, is added here; it passes
alone and fails when the rest of its file runs in one process against a forwarded
X display, which points at Qt tests competing for focus rather than at the
widget. It skips in CI, which installs pydm but no Qt binding.