feat(auth): init Authlib + provider LinkedIn (config env) (#88)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/auth/oauth.py

@@ -0,0 +1,21 @@
+import os
+
+from authlib.integrations.flask_client import OAuth
+from flask import Flask
+
+LINKEDIN_DISCOVERY_URL = (
+    "https://www.linkedin.com/oauth/.well-known/openid-configuration"
+)
+
+oauth = OAuth()
+
+
+def init_oauth(app: Flask) -> None:
+    oauth.init_app(app)
+    oauth.register(
+        name="linkedin",
+        client_id=os.getenv("LINKEDIN_CLIENT_ID"),
+        client_secret=os.getenv("LINKEDIN_CLIENT_SECRET"),
+        server_metadata_url=LINKEDIN_DISCOVERY_URL,
+        client_kwargs={"scope": "openid profile email"},
+    )