feat: Authorization Code Flow (KK) + session middleware + dev-login

- src/auth.js: OIDC mode (KC_CLIENT_ID/KC_CLIENT_SECRET), session-based
  middleware, legacy jwt-cookie migration, httpGet/httpPost без внешних зав.
- src/routes/auth.js: GET /callback (OIDC), GET+POST /dev-login (backdoor),
  session-based login/logout для обоих режимов
- server.js: express-session (8h, httpOnly, sameSite lax), trust proxy в prod
- views/dev-login.ejs: форма с пресетами MOCK_USERS + произвольные поля
- views/login.ejs: ссылка на /dev-login если devLoginEnabled
- tests: +5 тестов (session middleware), 50 PASS / 0 FAIL

Env-переменные:
  KC_CLIENT_ID, KC_CLIENT_SECRET, KC_BASE_URL, APP_URL  — OIDC режим
  SESSION_SECRET                                         — секрет сессии
  DEV_MODE=true                                          — /dev-login без пароля
  DEV_SECRET=xyz                                         — /dev-login с ?key=xyz

package-lock.json

@@ -14,6 +14,7 @@
         "ejs": "^3.1.10",
         "express": "^4.21.1",
         "express-rate-limit": "^8.5.2",
+        "express-session": "^1.19.0",
         "helmet": "^8.2.0",
         "jsonwebtoken": "^9.0.3",
         "pg": "^8.13.1"
@@ -360,6 +361,28 @@
         "express": ">= 4.11"
       }
     },
+    "node_modules/express-session": {
+      "version": "1.19.0",
+      "resolved": "https://registry.npmjs.org/express-session/-/express-session-1.19.0.tgz",
+      "integrity": "sha512-0csaMkGq+vaiZTmSMMGkfdCOabYv192VbytFypcvI0MANrp+4i/7yEkJ0sbAEhycQjntaKGzYfjfXQyVb7BHMA==",
+      "dependencies": {
+        "cookie": "~0.7.2",
+        "cookie-signature": "~1.0.7",
+        "debug": "~2.6.9",
+        "depd": "~2.0.0",
+        "on-headers": "~1.1.0",
+        "parseurl": "~1.3.3",
+        "safe-buffer": "~5.2.1",
+        "uid-safe": "~2.1.5"
+      },
+      "engines": {
+        "node": ">= 0.8.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/express"
+      }
+    },
     "node_modules/filelist": {
       "version": "1.0.6",
       "resolved": "https://registry.npmjs.org/filelist/-/filelist-1.0.6.tgz",
@@ -743,6 +766,14 @@
         "node": ">= 0.8"
       }
     },
+    "node_modules/on-headers": {
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/on-headers/-/on-headers-1.1.0.tgz",
+      "integrity": "sha512-737ZY3yNnXy37FHkQxPzt4UZ2UWPWiCZWLvFZ4fu5cueciegX0zGPnrlY6bwRg4FdQOe9YU8MkmJwGhoMybl8A==",
+      "engines": {
+        "node": ">= 0.8"
+      }
+    },
     "node_modules/parseurl": {
       "version": "1.3.3",
       "resolved": "https://registry.npmjs.org/parseurl/-/parseurl-1.3.3.tgz",
@@ -903,6 +934,14 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/random-bytes": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/random-bytes/-/random-bytes-1.0.0.tgz",
+      "integrity": "sha512-iv7LhNVO047HzYR3InF6pUcUsPQiHTM1Qal51DcGSuZFBil1aBBWG5eHPNek7bvILMaYJ/8RU1e8w1AMdHmLQQ==",
+      "engines": {
+        "node": ">= 0.8"
+      }
+    },
     "node_modules/range-parser": {
       "version": "1.2.1",
       "resolved": "https://registry.npmjs.org/range-parser/-/range-parser-1.2.1.tgz",
@@ -1111,6 +1150,17 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/uid-safe": {
+      "version": "2.1.5",
+      "resolved": "https://registry.npmjs.org/uid-safe/-/uid-safe-2.1.5.tgz",
+      "integrity": "sha512-KPHm4VL5dDXKz01UuEd88Df+KzynaohSL9fBh096KWAxSKZQDI2uBrVqtvRM4rwrIrRRKsdLNML/lnaaVSRioA==",
+      "dependencies": {
+        "random-bytes": "~1.0.0"
+      },
+      "engines": {
+        "node": ">= 0.8"
+      }
+    },
     "node_modules/unpipe": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/unpipe/-/unpipe-1.0.0.tgz",