fix: rebind selected workspace before db command startup

[julianknutsen]

Summary

• rebind db-targeted commands to the selected workspace before migration, store open, and dolt/server setup
• keep no-store commands consistent with explicit --db and selector env precedence
• add regression coverage for target config/env rebinding, no-db command behavior, dolt target selection, init guard mode detection, and external BEADS_DIR config isolation

Root cause

bd resolved the target workspace for DB commands too late. Global config and ambient caller state could leak into commands targeting another workspace, which let dolt server mode, auto-start settings, and config values come from the caller repo instead of the selected repo.

Testing

• go test ./cmd/bd -count=1
• make test
• golangci-lint run ./cmd/bd/... ./internal/config/...

Notes

• I ran this through repeated review/fix passes locally and addressed the blocker/major findings that surfaced during review.

[julianknutsen]

Tracking down some gnarly rogue dbs in gascity and I think this may be one of the culprits.