Drop the +1 last-column width reclaim

The MESHTERM_FULL_WIDTH reclaim reported the terminal one column wider than
probed, to draw a final column some terminals under-report. With the emoji
width now aligned to the terminal, that extra column pushes the frame past the
real screen edge and tears the layout. Remove it: the size probe is used as-is
again (_WidthExtendedOutput, _RECLAIM_LAST_COLUMN, _resolve_output, and the
MESHTERM_FULL_WIDTH gate all gone), and the app renders to prompt_toolkit's
default output. Drops tests/test_session_width.py with the feature.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_session_width.py

@@ -1,52 +0,0 @@
-"""Session width tests: reclaiming the terminal's final column.
-
-Some terminals (and prompt_toolkit's size probe on them) report the window one column
-narrower than it really is, so the frame's right border lands one short and the true last
-column sits unused. The session can report one extra column to close that gap. The wrapping
-output is pure and the resolver is a small branch, so both are assertable without a terminal.
-"""
-
-from __future__ import annotations
-
-from types import SimpleNamespace
-
-from prompt_toolkit.data_structures import Size
-
-import meshterm.ui.tui.session as session_mod
-from meshterm.ui.tui.session import TuiSession, _WidthExtendedOutput
-
-
-def test_width_extended_output_reports_one_more_column() -> None:
-    """get_size() gains a column; every other attribute forwards to the wrapped output."""
-    inner = SimpleNamespace(
-        get_size=lambda: Size(rows=24, columns=80),
-        write=lambda s: f"wrote:{s}",
-        encoding="utf-8",
-    )
-    out = _WidthExtendedOutput(inner)
-    assert out.get_size() == Size(rows=24, columns=81)  # the reclaimed column
-    assert out.write("x") == "wrote:x"  # forwarded method
-    assert out.encoding == "utf-8"      # forwarded attribute
-
-
-def test_session_leaves_a_supplied_output_untouched() -> None:
-    """A test-supplied output is never wrapped — headless sizes stay exactly as set."""
-    dummy = SimpleNamespace(get_size=lambda: Size(rows=10, columns=40))
-    session = TuiSession(output=dummy)
-    assert session._resolve_output() is dummy
-
-
-def test_session_wraps_the_real_terminal_when_enabled(monkeypatch) -> None:
-    """No supplied output + gate on → the real terminal output is width-extended."""
-    fake = SimpleNamespace(get_size=lambda: Size(rows=30, columns=100))
-    monkeypatch.setattr("prompt_toolkit.output.defaults.create_output", lambda: fake)
-    monkeypatch.setattr(session_mod, "_RECLAIM_LAST_COLUMN", True)
-    out = TuiSession()._resolve_output()
-    assert isinstance(out, _WidthExtendedOutput)
-    assert out.get_size() == Size(rows=30, columns=101)
-
-
-def test_session_gate_off_uses_the_bare_terminal(monkeypatch) -> None:
-    """Gate off → the real terminal output is used untouched (pt builds its own)."""
-    monkeypatch.setattr(session_mod, "_RECLAIM_LAST_COLUMN", False)
-    assert TuiSession()._resolve_output() is None