Add agent MCP profiles

[jorisjonkers-dev-agents]

Summary

• adds bounded Claude and Codex MCP profile fragments for minimal, frontend, cluster, code-intel, and full-diagnostic agent runs
• teaches the runner entrypoint to select profiles with AGENT_MCP_PROFILE while preserving explicit file overrides and legacy fallbacks
• wires assistant-api runner pods to default to the minimal MCP profile via AGENT_RUNTIME_DEFAULT_MCP_PROFILE
• adds platform coverage for profile contents and tool-count caps

Verification

• ./gradlew :platform:tooling:test --tests com.jorisjonkers.personalstack.platform.PlatformAgentMcpFluxTest
• ./gradlew :platform:tooling:runKtlintCheckOverTestSourceSet
• ./gradlew :services:assistant-api:test :services:assistant-api:runKtlintCheckOverMainSourceSet
• git diff --check

Known unrelated local drift

• Full :platform:tooling:test currently fails on pre-existing platform drift outside this change, including CI workflow coverage, observability/vault Flux expectations, inventory assertions, Samba Nix assertions, and stateless app image expectations. The targeted MCP profile platform test passes.