Split live-status tracking into its own subscriber (and share one MQTT connection) - Part 2: Add LiveStatusSubscriber

[n-lark]

Description

Gives live status its own LiveStatusSubscriber instead of bundling it into the team-channel subscriber, and has the two share one team MQTT connection (using the attach/detach from PR 1) rather than each needing its own.

Cut from #7843

See test plan: #7608 (comment)

Related Issue(s)

Resolves #7608

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

❌ Patch coverage is 90.08264% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.61%. Comparing base (56c95c3) to head (f55f01c).
⚠️ Report is 37 commits behind head on main.

Files with missing lines	Patch %	Lines
forge/ee/lib/sso/index.js	79.10%	14 Missing ⚠️
forge/lib/nonceStore.js	87.50%	5 Missing ⚠️
forge/ee/routes/expert/index.js	94.33%	3 Missing ⚠️
...orge/db/migrations/20260714-01-add-audit-source.js	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7844      +/-   ##
==========================================
+ Coverage   75.11%   75.61%   +0.49%     
==========================================
  Files         430      432       +2     
  Lines       22846    23035     +189     
  Branches     6055     6107      +52     
==========================================
+ Hits        17160    17417     +257     
+ Misses       5686     5618      -68     

Flag	Coverage Δ
backend	75.61% <90.08%> (+0.49%)	⬆️

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[cstns]

Looks good to me. The only thing i'd like to touch base on is the naming issue I mentioned on the pr this is based off of.

Other than that, happy to merge