ui: Drop classic decorators and migrate to single-file components (GJS)

[aklkv]

Description

This PR migrates the majority of Nomad UI components from the legacy split-file format (.js + .hbs) into co-located GJS (Glimmer JS) single-file components (.gjs). This removes the classic decorator patterns and consolidates template + logic into a single file per component, improving colocation, readability, and alignment with modern Ember conventions.

Summary of Changes

Single-File Component (GJS) Migration

Migrated 70+ components from split .js/.hbs format to single-file .gjs, including:

• Layout components: page-layout, global-header, gutter-menu
• UI primitives: toggle, stepper-input, two-step-button, copy-button, loading-spinner
• Data visualization: topo-viz, flex-masonry, chart-primitives, scale-events-chart
• Job pages: job-editor, job-version, job-page/service, job-status panels
• Allocation/Task: allocation-service-sidebar, task-sub-row, task-subnav
• Navigation: breadcrumbs, region-switcher, subnav components
• Forms: variable-form, policy-editor, token-editor
• File system: fs components
• DAS (recommendations): das components

Bug Fixes & Reactivity

• Fixed client metadata edit/add reactivity
• Fixed task row actions regression
• Avoided EmberObject.get in logger helper (use native property access)
• Normalized did-update modifier imports across components

Test Updates

• Updated integration tests to match new GJS component APIs
• Co-located test helpers with their respective component tests

Testing & Reproduction steps

All existing tests pass after migration. No new features or behavioral changes—this is a refactoring/modernization PR only.

Links

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad product documentation, which is stored in the
  web-unified-docs repo. Refer to the web-unified-docs contributor guide for docs guidelines.
  Please also consider whether the change requires notes within the upgrade
  guide. If you would like help with the docs, tag the nomad-docs team in this PR.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.