Triage: Add scope-aware memory providers

[time-attack]

Tracking the change proposed in #700 (by @16francej).

We're moving this from a code PR to a tracked issue under CONTRIBUTING.md: feature ideas belong in adrs/ as a short human-written note and bugs as an issue, and we implement the underlying code from our side. Capturing the original proposal here so it isn't lost.

Original PR: #700
Reported by: @16francej

---

Add scope-aware memory routing so deployments can combine the built-in notebook with external MCP-backed providers and independently configure recall, explicit writes, automatic capture, and management by scope.

• passes query and acting-user context into recall
• supports separate read/write OAuth credentials, bounded calls, and fail-open recall
• preserves existing notebook behavior by default
• verification: focused memory/config/MCP tests, typechecks, lint, and orchestrator suite

Implements the direction proposed in #600.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}

---

If we ship a fix or feature from this, credit @16francej as co-author.