Remove internal sd-server management, proxy to external sd-server

- Remove ProcessManager and process.py
- Add get_sd_server_url() config (env/config/default)
- Update routes to proxy to external sd-server URL
- Remove model switching (handled by external sd-server)
- Update CLI serve command
- Update tests for new architecture

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/reinstall.py

@@ -55,9 +55,17 @@ def sync_to_junkpile() -> None:
     """Sync project to junkpile."""
     print("\n[3/4] Syncing to junkpile...")
     excludes = [
-        ".git", ".venv", "__pycache__", "*.pyc", ".mypy_cache",
-        ".pytest_cache", ".ruff_cache", ".coverage", "*.egg-info",
-        "node_modules", ".tmp",
+        ".git",
+        ".venv",
+        "__pycache__",
+        "*.pyc",
+        ".mypy_cache",
+        ".pytest_cache",
+        ".ruff_cache",
+        ".coverage",
+        "*.egg-info",
+        "node_modules",
+        ".tmp",
     ]
     cmd = ["rsync", "-avz", "--delete"]
     for exc in excludes: