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.

src/textual_webterm/app_session.py

@@ -140,8 +140,8 @@ class AppSession(Session):
         environment["TEXTUAL_DRIVER"] = "textual.drivers.web_driver:WebDriver"
         environment["TEXTUAL_FPS"] = "60"
         environment["TEXTUAL_COLOR_SYSTEM"] = "truecolor"
-        environment["TERM_PROGRAM"] = "textual-web"
-        environment["TERM_PROGRAM_VERSION"] = version("textual-web")
+        environment["TERM_PROGRAM"] = "textual-webterm"
+        environment["TERM_PROGRAM_VERSION"] = version("textual-webterm")
         environment["COLUMNS"] = str(width)
         environment["ROWS"] = str(height)
         if self.devtools: