[T612] Fix non-mutating roleful target semantics

[ai21z]

Summary

• Render non-mutating expected target hints as evidence roles instead of mutation obligations in local turn traces
• Reuse the same roleful projection for prompt-debug target roles
• Add trace and prompt-debug regressions for read-only existence prompts

Verification

• RED: LocalTurnTracePolicyTraceTest.readOnlyPolicyTraceDoesNotRenderTargetHintsAsMutationObligations failed before implementation
• RED: PromptDebugInspectorTargetRolesTest.promptDebugDoesNotShowReadOnlyTargetHintsAsMustMutate failed before implementation
• ./gradlew.bat test --tests "dev.talos.runtime.trace.LocalTurnTracePolicyTraceTest" --no-daemon
• ./gradlew.bat test --tests "dev.talos.cli.prompt.PromptDebugInspectorTargetRolesTest" --no-daemon
• ./gradlew.bat test --tests "dev.talos.runtime.task.*" --no-daemon
• ./gradlew.bat test --tests "dev.talos.runtime.trace.*" --no-daemon
• ./gradlew.bat test --tests "dev.talos.cli.prompt.*" --no-daemon
• ./gradlew.bat test --tests "dev.talos.runtime.toolcall.ExpectedTargetProgressAccountingTest" --no-daemon
• git diff --check
• ./gradlew.bat validateArchitectureBoundaries --no-daemon
• ./gradlew.bat check --no-daemon