docs: update guidelines for Svelte module changes and linting requirements

- Enhanced documentation in AGENTS.md and web/README.md to clarify the mandatory steps for running `npm run check` and `npm run lint` before finalizing changes in the `web/**` directory.
- Updated engineering rules in .cursor/rules/engineering.mdc to specify the necessity of both commands and the use of Prettier for formatting issues.
- Added detailed instructions for handling linting failures and emphasized the importance of these checks in CI workflows.

scripts/lint-web.ps1

@@ -0,0 +1,5 @@
+# Same gates as CI job web (.gitea/workflows/ci.yaml).
+$ErrorActionPreference = 'Stop'
+Set-Location (Join-Path $PSScriptRoot '..' 'web')
+npm run check
+npm run lint

scripts/lint-web.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+# Same gates as CI job web (.gitea/workflows/ci.yaml).
+set -euxo pipefail
+cd "$(dirname "$0")/../web"
+npm run check
+npm run lint