Add custom SVG exporter, remove Rich from screenshot rendering

- Created svg_exporter.py with direct pyte-to-SVG rendering
- Eliminates Rich's export_svg() quirks (clip path count mismatch)
- Added 63 comprehensive tests for SVG exporter
- Removed Rich imports from local_server.py, terminal_session.py,
  app_session.py, and cli.py
- Replaced RichHandler with standard logging.basicConfig
- Replaced @rich.repr.auto with standard __repr__ methods
- Rich is no longer directly imported (still transitive via textual-serve)

Bump version to 0.3.0

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "textual-webterm"
-version = "0.2.10"
+version = "0.3.0"
 description = "Serve terminal sessions over the web"
 authors = ["Will McGugan <will@textualize.io>"]
 license = "MIT"