Refactor tool schema default handling and error responses for consistency across MCP tools

[cstns]

Description

Related Issue(s)

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 96.29630% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 76.85%. Comparing base (d9e8d19) to head (ad7c5a9).

Files with missing lines	Patch %	Lines
forge/comms/platformAutomation.js	88.88%	1 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                          @@
##           feat/extend-mcp-tool-feature-set    #8287      +/-   ##
====================================================================
+ Coverage                             76.78%   76.85%   +0.07%     
====================================================================
  Files                                   458      458              
  Lines                                 24395    24374      -21     
  Branches                               6478     6474       -4     
====================================================================
+ Hits                                  18732    18733       +1     
+ Misses                                 5663     5641      -22     

Flag	Coverage Δ
backend	76.85% <96.29%> (+0.07%)	⬆️

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[andypalmi]

Fixed here, all check out:

• limit/page required-despite-default: genuine zod chaining-order gotcha (.optional().default(x) vs .default(x).optional()), nice catch, and the new catalog_spec.js invariant test guards against it recurring on a future tool.
• getLiveCachedState(args.hostedInstanceId) → getLiveCachedState(device.id) in devices.js: real bug, not a style change - every row in a device list was hitting the same wrong cache key before this.
• platform_get_remote_instance_status description: now matches what the handler actually does (cache-first, MQTT only on a miss), the old description was just wrong.
• platform_create_remote_instance_snapshot removal: genuine duplicate, platform_create_instance_snapshot already covers instanceType: 'remote' against the same endpoint.
• platform_get_current_user removal: genuine duplicate of platform_get_active_user, no other references to it anywhere in the repo.

Still open from the report, not touched by this PR:

• Reversed logs pagination direction
• Double-encoded includeStatus errors
• Inconsistent hostedInstanceId validation across tools
• count meaning different things depending on scope
• platform_get_active_browser_session annotated as a write tool
• sort/orderByMostRecentFlows duplication
• Inconsistent teamId descriptions
• Missing idempotentHint/openWorldHint annotations
• Hand-copied STATE_GROUPS

Nothing here is made worse by this PR, just not addressed yet.

Want to keep going on those in this PR, split them into another one, or should I put together a PR on top of this one that merges into base once it lands?