[Implementation] Quiet benign guardrail notices

[aponcedeleonch]

Summary

Make routine successful contextual guardrail inspections quiet by default in mecatui while preserving actionable outcomes.

• classify only exact structured complete + acceptable + (execute | release_result) reviews with valid review identity/job as benign
• retain benign hook summaries and live detail blocks, hiding them only in collapsed presentation
• reveal retained benign notices with ctrl+t
• add client setting hook_notices.show_benign: true
• bind asynchronous details to the requesting session and review ID; stale responses are discarded and mismatches fail visibly
• keep approval details isolated on their matching approval surface

Stack

• Plan / Interface: [Plan / Interface] Quiet benign guardrail notices #1957
• This PR targets plan/quiet-benign-hook-notices

Verification

Passed:

• focused mecatui, client, and UI tests
• changed-package race tests
• task lint
• task docs
• task site:build
• task ac-trace-strict
• offline mecademo
• panel review; all findings addressed

Known unrelated baseline failure:

• task test and task test:race reproduce TestMecak8sHelmChart_DeployCheckProductionFixtureRuntimeAndSpread: rendered namespace is toolhive-system, while the existing fixture expects default. This stack does not modify Helm files.