Add a read-only web viewer for sessions and traces

[aurexav]

Context
ELF has strong retrieval primitives (search sessions, traces, and explain outputs), but debugging and operational usage are currently API-first. A lightweight web viewer would shorten the loop for evaluation and tuning.

Goal
Provide a small read-only UI to browse notes and inspect retrieval sessions and traces during development.

Scope (read-only)

• Search sessions: view a session index, build the timeline view, and fetch details for selected notes.
• Notes: view note metadata (type/key, scope, importance/confidence, timestamps, TTL/expires, hit_count/last_hit_at) and source_ref.
• Traces: view trace metadata (expanded queries, candidate_count, config snapshot) and per-item explain fields.
• Admin-only: the viewer must talk to the admin bind and must not be exposed on the public bind by default.

Non-goals

• Authentication and authorization.
• Editing, deleting, or bulk export.
• Hosted deployment.

Acceptance criteria

• A developer can run the viewer locally and reproduce a full workflow: search -> pick note ids -> view details -> inspect explain.
• The viewer renders correctly on mobile and desktop.

Priority
Deferred (post retrieval-v2).

References

• claude-mem viewer UX (inspiration only)