fix: platform automation context missing applicationId/instanceId on device pages

[andypalmi]

Closes FlowFuse/engineering#214

Where the issue was

useContextStore's expert getter (frontend/src/stores/context.js) builds the context object sent with every chat query and returned by the ui_get_context automation tool. applicationId and instanceId were both derived by string-matching the current route (/applications/, /instance/) and reading route.params.id - which is never true on a device-overview page, so both came back null whenever a device was open, even though the device has a known owning application or instance. The same route-string approach also missed state.application, which application-overview pages already populate, and missed device-group pages entirely (:applicationId/device-group/:deviceGroupId, which never registered anything with the context store and use a differently-named route param).

How it's fixed

• applicationId now prefers the owning application already loaded on state.device/state.instance, then state.application, before falling back to the route-string check.
• instanceId now prefers the owning instance loaded on state.device before falling back to the same route-string check.
• application/DeviceGroup/index.vue registers its loaded application with the context store (mirroring what the application-overview page already does), fixing the missing-param-name case.
• device/index.vue now also registers the device's actual owner (application or instance) directly with the context store, matching the pattern application/instance overview pages already use for themselves.
• The context now includes deviceOwnerType so a device directly owned by an application can be told apart from one owned by an instance without inferring it from which ID happens to be present.

Test plan

• Device owned directly by an application: ui_get_context and the chat context return the device's actual applicationId (previously null).
• Device owned by an instance: instanceId (previously null) and the instance's owning applicationId are both returned, with deviceOwnerType: "instance" disambiguating the two IDs.
• Application-overview page and its nested tabs.
• Device-group page under an application.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.86%. Comparing base (ca3c665) to head (5490cab).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7995   +/-   ##
=======================================
  Coverage   75.86%   75.86%           
=======================================
  Files         434      434           
  Lines       23340    23340           
  Branches     6209     6209           
=======================================
  Hits        17708    17708           
  Misses       5632     5632           

Flag	Coverage Δ
backend	75.86% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.