feat: Add OIDC authentication with Authentik integration

- Add OIDC login flow with Authentik provider
- Implement session-based auth with Redis store
- Add avatar display from OIDC claims
- Fix input field performance with react-textarea-autosize
- Stabilize callbacks to prevent unnecessary re-renders
- Fix history loading to skip empty session files
- Add 2-row default height for input textarea

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/package-lock.json

@@ -13,6 +13,7 @@
         "react-dom": "^18.2.0",
         "react-markdown": "^10.1.0",
         "react-syntax-highlighter": "^16.1.0",
+        "react-textarea-autosize": "^8.5.9",
         "remark-gfm": "^4.0.1"
       },
       "devDependencies": {
@@ -3535,6 +3536,22 @@
         "react": ">= 0.14.0"
       }
     },
+    "node_modules/react-textarea-autosize": {
+      "version": "8.5.9",
+      "resolved": "https://registry.npmjs.org/react-textarea-autosize/-/react-textarea-autosize-8.5.9.tgz",
+      "integrity": "sha512-U1DGlIQN5AwgjTyOEnI1oCcMuEr1pv1qOtklB2l4nyMGbHzWrI0eFsYK0zos2YWqAolJyG0IWJaqWmWj5ETh0A==",
+      "dependencies": {
+        "@babel/runtime": "^7.20.13",
+        "use-composed-ref": "^1.3.0",
+        "use-latest": "^1.2.1"
+      },
+      "engines": {
+        "node": ">=10"
+      },
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      }
+    },
     "node_modules/read-cache": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/read-cache/-/read-cache-1.0.0.tgz",
@@ -4112,6 +4129,48 @@
         "browserslist": ">= 4.21.0"
       }
     },
+    "node_modules/use-composed-ref": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/use-composed-ref/-/use-composed-ref-1.4.0.tgz",
+      "integrity": "sha512-djviaxuOOh7wkj0paeO1Q/4wMZ8Zrnag5H6yBvzN7AKKe8beOaED9SF5/ByLqsku8NP4zQqsvM2u3ew/tJK8/w==",
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@types/react": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/use-isomorphic-layout-effect": {
+      "version": "1.2.1",
+      "resolved": "https://registry.npmjs.org/use-isomorphic-layout-effect/-/use-isomorphic-layout-effect-1.2.1.tgz",
+      "integrity": "sha512-tpZZ+EX0gaghDAiFR37hj5MgY6ZN55kLiPkJsKxBMZ6GZdOSPJXiOzPM984oPYZ5AnehYx5WQp1+ME8I/P/pRA==",
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@types/react": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/use-latest": {
+      "version": "1.3.0",
+      "resolved": "https://registry.npmjs.org/use-latest/-/use-latest-1.3.0.tgz",
+      "integrity": "sha512-mhg3xdm9NaM8q+gLT8KryJPnRFOz1/5XPBhmDEVZK1webPzDjrPk7f/mbpeLqTgB9msytYWANxgALOCJKnLvcQ==",
+      "dependencies": {
+        "use-isomorphic-layout-effect": "^1.1.1"
+      },
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      },
+      "peerDependenciesMeta": {
+        "@types/react": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/util-deprecate": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/util-deprecate/-/util-deprecate-1.0.2.tgz",