feat: Allow /resume to accept session names, not just UUIDs

Summary

When naming a session, users should be able to resume it by that name instead of needing to use the UUID.

Current Behavior

1. User names a session (e.g., "Jan 26 Katib and Whisper Issues")
2. The name is stored in sessions-index.json under the summary field
3. To resume, user must use the UUID: /resume 1a2b1875-bdcc-457b-a8a2-5f3fe51d15d4
4. Attempting /resume Jan 26 Katib and Whisper Issues fails with "Session not found"

Expected Behavior

/resume should support:

• Exact name match: /resume "Jan 26 Katib and Whisper Issues"
• Fuzzy/partial match: /resume Katib (if unambiguous)
• Continue supporting UUIDs for backwards compatibility

Rationale

If users can name sessions, they should be able to reference them by name. Requiring users to look up and copy UUIDs defeats the purpose of naming sessions in the first place.

Suggested Implementation

When /resume <arg> is called:

1. First check if <arg> is a valid UUID - if so, use existing behavior
2. Otherwise, search session summaries for matches
3. If exactly one match, resume that session
4. If multiple matches, show disambiguation list
5. If no matches, show "Session not found" with suggestions