Harden guideline capability mapping

[chubes4]

Summary

• Adds explicit guideline/memory capabilities and scope metadata for private user-workspace memory and workspace-shared guidance.
• Maps private memory reads/edits through owner metadata instead of core private-post semantics.
• Documents capability behavior and extends smoke coverage for owner-only private memory, shared guidance thresholds, and promotion gating.

Tests

• php tests/guidelines-substrate-smoke.php
• homeboy lint --path /Users/chubes/Developer/agents-api@chubes-guideline-capabilities
• homeboy test --path /Users/chubes/Developer/agents-api@chubes-guideline-capabilities

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Implementing guideline capability mapping, smoke tests, documentation, and local verification. Chris remains responsible for review and submission.

Fixes #62