Add read-only regression coverage for aliases and toolsets

[davidahmann]

Problem
Read-only filtering already covers dynamic toolsets and deprecated aliases, but there was no dedicated regression coverage for those two paths, so a future inventory change could silently re-expose write tools.

Why now
Issue #2192 narrowed this to test coverage after confirming the current runtime is already fail-closed. The gap is in preserving that contract.

What changed

• add a dedicated ToolsForToolset read-only regression test for dynamic toolset enablement
• add a deprecated-alias read-only regression test for ForMCPRequest

Validation

• go test ./pkg/inventory -run 'TestToolsForToolset_RespectsReadOnly|TestForMCPRequest_ToolsCall_DeprecatedAliasRespectsReadOnly'

Refs #2192

[davidahmann]

User impact: This locks in the current fail-closed behavior so future inventory changes do not silently re-expose write tools through dynamic toolsets or deprecated aliases.
Change: The change is regression coverage only: one test for read-only ToolsForToolset, and one for deprecated alias filtering through ForMCPRequest.
Validation:

• go test ./pkg/inventory -run 'TestToolsForToolset_RespectsReadOnly|TestForMCPRequest_ToolsCall_DeprecatedAliasRespectsReadOnly' passed

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