Implement bd restore command and flip ready work sort order

- Add bd restore command to view full history of compacted issues from git
- Command temporarily checks out historical commit, reads JSONL, displays original content
- Read-only operation, no database or git state modification
- Flip ready work sort to created_at ASC (older issues first within priority tier)
- Prevents issue treadmill effect, surfaces old P1s for triage
- Update README.md and AGENTS.md with restore documentation

Closes bd-407, bd-383

AGENTS.md

@@ -57,6 +57,9 @@ bd show <id> --json
 bd rename-prefix kw- --dry-run  # Preview changes
 bd rename-prefix kw- --json     # Apply rename
 
+# Restore compacted issue from git history
+bd restore <id>  # View full history at time of compaction
+
 # Import with collision detection
 bd import -i .beads/issues.jsonl --dry-run             # Preview only
 bd import -i .beads/issues.jsonl --resolve-collisions  # Auto-resolve