build: add pyte and measure subprocess coverage

pyte is a VT100 emulator; the curses tests will run pqcli in a
pseudo-terminal and read the rendered screen through it.

Coverage now also measures the pqcli processes the tests start, so the
curses UI and the existing CLI subprocess tests count towards the
report.

pyproject.toml

@@ -37,7 +37,7 @@ requires = ["hatchling"]
 build-backend = "hatchling.build"
 
 [dependency-groups]
-dev = ["prek>=0.2", "pytest>=8.0", "ty>=0.0.89"]
+dev = ["prek>=0.2", "pyte>=0.8", "pytest>=8.0", "ty>=0.0.89"]
 
 [tool.ty.src]
 # Only the package and its tests; agent worktrees under .claude/ would
@@ -52,3 +52,8 @@ select = ["E", "F", "W", "I", "UP"]
 
 [tool.ruff.lint.isort]
 known-first-party = ["pqcli"]
+
+[tool.coverage.run]
+# Also measure the pqcli processes the tests start, such as the curses
+# UI driven through a pseudo-terminal.
+patch = ["subprocess"]