refactor(url): remove automatic trailing slash stripping from base URL inputs

- Remove `.replace(/\/+$/, "")` from all base URL handlers in useBaseUrlState.ts
- Remove trailing slash stripping in useCodexConfigState.ts
- Remove trailing slash normalization in providerConfigUtils.ts setCodexBaseUrl()
- Update i18n hints (en/ja/zh) to instruct users to avoid trailing slashes

This gives users explicit control over URL format rather than silently modifying input.

src/i18n/locales/en.json

@@ -272,7 +272,7 @@
     "fastModel": "Fast Model (optional)",
     "fastModelPlaceholder": "e.g., GLM-4.5-Air",
     "modelHint": "💡 Leave blank to use provider's default model",
-    "apiHint": "💡 Fill in Claude API compatible service endpoint",
+    "apiHint": "💡 Fill in Claude API compatible service endpoint, avoid trailing slash",
     "codexApiHint": "💡 Fill in service endpoint compatible with OpenAI Response format",
     "fillSupplierName": "Please fill in provider name",
     "fillConfigContent": "Please fill in configuration content",

src/i18n/locales/ja.json

@@ -272,7 +272,7 @@
     "fastModel": "高速モデル（任意）",
     "fastModelPlaceholder": "例: GLM-4.5-Air",
     "modelHint": "💡 空欄ならプロバイダーのデフォルトモデルを使用します",
-    "apiHint": "💡 Claude API 互換サービスのエンドポイントを入力してください",
+    "apiHint": "💡 Claude API 互換サービスのエンドポイントを入力してください。末尾にスラッシュを付けないでください",
     "codexApiHint": "💡 OpenAI Response 互換のサービスエンドポイントを入力してください",
     "fillSupplierName": "プロバイダー名を入力してください",
     "fillConfigContent": "設定内容を入力してください",

src/i18n/locales/zh.json

@@ -272,7 +272,7 @@
     "fastModel": "快速模型 (可选)",
     "fastModelPlaceholder": "例如: GLM-4.5-Air",
     "modelHint": "💡 留空将使用供应商的默认模型",
-    "apiHint": "💡 填写兼容 Claude API 的服务端点地址",
+    "apiHint": "💡 填写兼容 Claude API 的服务端点地址，不要以斜杠结尾",
     "codexApiHint": "💡 填写兼容 OpenAI Response 格式的服务端点地址",
     "fillSupplierName": "请填写供应商名称",
     "fillConfigContent": "请填写配置内容",