v0.3.0

The features the first real user's coverage study asked for, in the
order it ranked them, plus the terminal-query work that lets
capability-probing applications run against termlens unmodified.

Changed

• Scroll gained Left and Right variants and is now
  #[non_exhaustive]. Exhaustive match on it needs a wildcard arm;
  marking it non-exhaustive means later additions won't break code
  again.

Added

• Writes now respect the terminal's deadline. send, send_str,
  paste, click and scroll used to block indefinitely if the
  application stopped reading its input and the PTY buffer filled — the
  one place the crate's own "no unbounded waits" rule wasn't applied.
  They now fail at the deadline with the screen attached and a message
  naming the real cause, instead of hanging a CI job.
• A fuller mouse API: click_with(button, col, row) for middle and
  right buttons, drag(button, from, to), modifier chords
  (MouseButton::Left.ctrl(), mirroring Key::Right.ctrl()), and
  horizontal wheel via Scroll::Left / Scroll::Right. Everything
  stays mode-aware: encoded for the tracking mode and encoding the
  application enabled, and refused with a typed error when the mode
  cannot express the gesture — a drag under X10, which reports no
  release, is an error rather than a misleading half-gesture.
• termlens answers DECRQM ("is private mode n set?"), so an
  application that probes before using synchronized output enables it
  against termlens — wait_frame works against programs nobody
  modified for the harness. Replies are truthful or absent: modes whose
  state the emulator holds exactly report set/reset, everything else
  reports "not recognized" rather than a guess. DECRQSS, OSC 4
  palette reads and OSC 52 clipboard reads are now recognized too, so
  an application blocked on one is named in the timeout instead of
  hanging silently.
• TerminalBuilder::foreground_rgb configures the OSC 10 answer,
  which was hardcoded white. Applications that pick a theme by
  comparing foreground and background luminance can now be tested
  against both.
• Every wait now takes a per-call deadline: wait_frame_for,
  wait_idle_for and wait_exit_for join wait_until_for. One
  known-slow step no longer forces the builder timeout up for every
  other wait in the suite — which is what made a genuinely stuck
  application burn the long timeout on its first failure. Timeout errors
  report the deadline that actually applied.
• wait_frame retains the last 8 completed frames and evaluates
  them oldest first, so a burst of frames arriving in a single read is
  observable step by step — a progress counter ticking 1, 2, 3 in
  one write used to be visible only at 3. The retention bound and its
  two consequences (a longer burst drops its oldest frames; a retained
  frame stays matchable, so a predicate satisfied earlier resolves at
  once) are documented on wait_frame and in docs/DESIGN.md §2.