feat(nodes): expose policy-filtered discovery tool

[bogdanovich]

What changed or was removed

• Added a read-only nodes model tool with list and describe actions.
• Applied each agent's effective named-target policy before returning discovery data.
• Resolved live node state through the gateway registry while redacting raw node IDs, configured node references, public keys, aliases, and capability schemas.
• Registered the tool across startup and config reloads, including removal when nodes are disabled.

Why

The node companion MVP needs a bounded discovery surface before remote invocation is exposed. Agents should reason only about operator-owned target names and pairing-approved command summaries, never transport or identity details.

User and developer impact

Agents with an explicit target_policy can list their configured targets and inspect approved command names, risk classes, cancellation/progress support, platform, version, and health. Missing policies fail closed and expose no targets. This PR does not permit remote execution.

Validation

• go test -tags goolm,stdjson ./...
• golangci-lint run --allow-parallel-runners --build-tags=goolm,stdjson ./pkg/tools/... ./pkg/gateway/...
• go test -tags goolm,stdjson ./pkg/tools ./pkg/gateway
• git diff --check

Later PRs

• Add typed invoke, status, and cancel actions with durable human approval.
• Emit redacted node runtime audit events.
• Complete the node MVP audit and document intentional gaps.

[bogdanovich]

Automated review by Reviewer agent.

Review Summary

Direct inspection found no independently validated actionable defect, but the required Codex advisory analysis could not run because ACPx returned an internal runtime error.

Coverage Notes

• Required Codex advisory analysis was unavailable due to ACPx runtime failure; queue worker should treat this result as inconclusive rather than clean.

[bogdanovich]

/forgeclaw review