feat: add clickable monitor links

[anjupathak03]

Describe your changes

Adds an optional application URL to monitors so users can open the monitored application directly from its details page.

• adds linkUrl to the TypeScript monitor types, Mongo model, repository mapping, create/edit validation, JSON import/export shape, and API response schema
• adds an optional Application URL field to the shared monitor form, so the feature works for uptime, PageSpeed, and infrastructure monitors
• renders the application URL as a themed, underlined-on-hover link in the monitor header with an explanatory tooltip
• opens links in a new tab with noopener noreferrer
• accepts only HTTP(S) URLs, limits them to 2048 characters, and checks the protocol again before rendering
• adds validation coverage for valid local/public URLs, clearing the optional field, imports, malformed URLs, unsafe schemes, and overlong values

This revives the intent of #2456, which maintainers closed after the backend was substantially refactored and invited contributors to reimplement against develop.

Write your issue number after "Fixes "

Fixes #2454

Verification

• npm test -- --runInBand --coverage=false — 74 suites, 1333 tests passed
• npm test -- --runTestsByPath test/unit/validation/monitorValidation.test.ts --runInBand --coverage=false — 52 tests passed
• npm run build in server
• npm run typeCheck in server
• npm run lint in server
• npm run format-check in server and client
• npm run build in client
• strict ESLint with zero warnings on every changed client TypeScript/TSX file

Checklist

• I deployed the application locally. This is a draft pending final UI verification.
• I have performed a self-review and tested the change.
• I have included the issue number.
• New visible strings use i18n.
• I have not included unrelated files or dependency changes.
• No production styling values are hardcoded.
• Styling uses existing theme values and components.
• The PR is granular and targeted to one feature.
• Formatting was verified in both server and client.
• A screenshot will be added after final UI verification.