fix: repair broken tests and remove unused dependencies

Test fixes:
- Fix app_session.py to use 'textual-webterm' package name (not 'textual-web')
- Fix CLI version test to not hardcode version number
- Fix static path test to not use removed Path._flavour attribute

Removed unused dependencies:
- xdg
- msgpack
- httpx

All 209 tests pass with 86% coverage.

pyproject.toml

@@ -15,10 +15,7 @@ aiohttp = "^3.13.0"
 uvloop = { version = "^0.22.0", markers = "sys_platform != 'win32'" }
 click = "^8.1.7"
 pydantic = "^2.7.0"
-xdg = "^6.0.0"
-msgpack = "^1.1.0"
 importlib-metadata = ">=6.0.0"
-httpx = ">=0.27.0"
 tomli = { version = "^2.0.1", python = "<3.11" }
 pyyaml = "^6.0.0"
 pyte = "^0.8.0"