Add `source` column to sessions and messages ('claude' | 'codex').
Discover and parse Codex JSONL files from ~/.codex/sessions/, mapping
Codex thread/item structures to the same schema (messages, tool_calls,
tool_results, subagents). Move DB to ~/.obelisk/ with legacy migration.
Add rebuild-to-temp-then-swap for safe full rebuilds. On the app side:
source filter toggle, collapsible untitled session fold, configurable
codexDir in Settings, and a dev script. Update SKILL.md and query
helpers to expose source fields and accept source filter opt.
