* fix(orphans): honor --db flag for cross-repo orphan detection
Problem:
- `bd orphans --db /path` ignored the --db flag entirely
- FindOrphanedIssues() hardcoded local .beads/ directory
Solution:
- Introduce IssueProvider interface for abstract issue lookup
- Add StorageProvider adapter wrapping Storage instances
- Update FindOrphanedIssues to accept provider instead of path
- Wire orphans command to create provider from --db flag
Closes: steveyegge/beads#1196
* test(orphans): add cross-repo and provider tests for --db flag fix
- Add TestFindOrphanedIssues_WithMockProvider (table-driven, UT-01 through UT-09)
- Add TestFindOrphanedIssues_CrossRepo (validates --db flag honored)
- Add TestFindOrphanedIssues_LocalProvider (backward compat RT-01)
- Add TestFindOrphanedIssues_ProviderError (error handling UT-07)
- Add TestFindOrphanedIssues_IntegrationCrossRepo (IT-02 full)
- Add TestLocalProvider_* unit tests
Coverage for IssueProvider interface and cross-repo orphan detection.
* docs: add bd orphans command to CLI reference
Document the orphan detection command including the cross-repo
workflow enabled by the --db flag fix in this PR.