Distinguish default-disabled embeddings from explicit disable

[coderabbitai]

Summary

Add a default-disabled state to EmbeddingsStatus, or add an equivalent provenance flag. The session-start embeddings nudge must distinguish the seeded default configuration from an explicit hivemind embeddings disable opt-out.

Rationale

A fresh installation and an explicit disable currently both produce "user-disabled". The notification rule therefore cannot suppress the one-time nudge after an explicit user opt-out.

Affected areas

• src/user-config.ts: retain whether the disabled value came from the seeded default or an explicit user action.
• src/embeddings/disable.ts: expose the distinct status or provenance.
• src/notifications/index.ts and src/notifications/types.ts: pass the value into NotificationContext.
• src/notifications/rules/embeddings-nudge.ts: notify for the default-disabled case, but remain silent after explicit disable.
• Related tests for embeddings status and the session-start notification rule.

Acceptance criteria

• Fresh installations with the seeded disabled default can receive the embeddings nudge.
• hivemind embeddings disable produces a state that is distinguishable from the seeded default.
• The embeddings nudge does not emit after an explicit hivemind embeddings disable.
• The enabled state remains silent.
• Tests cover the default-disabled, explicit-disable, and enabled cases.

Backlinks

• Pull request: fix(recall): notify once at SessionStart when embeddings not installed #353
• Review comment: fix(recall): notify once at SessionStart when embeddings not installed #353 (comment)
• Requested by: @efenocchi