Configurable session limit for /resume picker

Problem

The /resume picker is hardcoded to display only the 50 most recent sessions. Power users accumulate hundreds of sessions (I have 488 .jsonl files across projects) and cannot access older conversations through the picker UI.

Prior issues

This has been requested multiple times, with all issues closed as duplicate or stale without resolution:

• #35698, #29052, #24777, #24435, #25130, #25729, #23375, #23072, #23933

The limit was previously raised from ~10 to 50, but there's still no way to configure it or paginate beyond it.

Proposed solution

One or more of:

• A configurable resumeLimit setting in settings.json
• Pagination / "load more" in the picker that actually works beyond the initial batch
• A --resume-limit N CLI flag

Workaround

Users can bypass the picker with claude --resume <session-id>, but discovering the session ID requires manually browsing .jsonl files on disk.