fix(auth): invalidate sessions when 2FA is enabled, fix dev 401 loop

Add UserService.BumpLoginEpoch and call it from updateSetting when
TwoFactorEnable flips false → true. Existing cookies (issued under
the looser no-2FA policy) get a 401 on their next request and are
forced through the login flow. Disabling 2FA is a relaxation and
does not bump the epoch — sessions stay valid.

Also fix the dev-mode 401 redirect: targeting `${basePath}login.html`
breaks when basePath isn't "/" (Vite has no file at e.g.
"/test/login.html"; the SPA fallback loops the 401). Navigate to
basePath instead — Vite's bypassMigratedRoute and Go's index
handler both serve login.html for that path.

Strip stale doc-comment from netsafe and IndexController.logout
in line with the project's no-inline-comments convention.

web/controller/setting.go

@@ -76,7 +76,13 @@ func (a *SettingController) updateSetting(c *gin.Context) {
 		jsonMsg(c, I18nWeb(c, "pages.settings.toasts.modifySettings"), err)
 		return
 	}
+	oldTwoFactor, twoFactorErr := a.settingService.GetTwoFactorEnable()
 	err = a.settingService.UpdateAllSetting(allSetting)
+	if err == nil && twoFactorErr == nil && !oldTwoFactor && allSetting.TwoFactorEnable {
+		if bumpErr := a.userService.BumpLoginEpoch(); bumpErr != nil {
+			err = bumpErr
+		}
+	}
 	jsonMsg(c, I18nWeb(c, "pages.settings.toasts.modifySettings"), err)
 }