feat: resolve Claude Code session names from JSONL transcripts

[kianwoon]

Summary

• Display human-readable session names in the GUI sessions section instead of only model IDs
• Auto-resolve names from Claude Code's ~/.claude/projects/ JSONL files, preferring customTitle (from /rename or --name)
• Use project directory name as fallback when no customTitle is set
• Support x-session-name header override via ANTHROPIC_CUSTOM_HEADERS
• Move model names to a separate line below session name, styled in light blue

Resolution priority

1. customTitle — user-set via /rename or --name (preferred)
2. Project directory name — derived from ~/.claude/projects/<encoded-path>
3. x-session-name header — manual override
4. No name — fallback to truncated session ID

Files changed

• src/session-pool.ts — lazy JSONL resolution, sessionNames cache, setName() API
• src/server.ts — extract x-session-name header
• src/ws.ts — merge name into WebSocket summary
• src/types.ts — add optional name to sessionStats type
• gui/frontend/app.js — split name and models into separate lines
• gui/frontend/styles.css — light blue session name (#7ec8e3), dim models line

Test plan

• Session with /rename → shows custom title (e.g. "Testing Session Name")
• Session without rename → shows project folder name (e.g. "swiftUI")
• x-session-name header override works
• TypeScript type check passes
• GUI rebuild successful