feat: enhance migration with Dolt support and comment mapping

[greghughespdx]

Summary

• sd migrate-from-beads now supports Dolt-based beads installations (v0.55+) in addition to legacy JSONL
• Comments are mapped during migration (beads text field to seeds body field)

Context

Beads v0.55+ moved from JSONL storage to Dolt, making the existing JSONL-only migration path unreachable for modern installations. This adds automatic detection: if .beads/issues.jsonl exists, it reads from that (legacy path). If only .beads/ directory exists and the bd CLI is available, it shells out to bd list --json and bd show --json to extract all issues with comments.

Changes

• src/commands/migrate.ts: Added loadFromDolt() function, BeadsComment interface, comment mapping in mapBeadsIssue(), auto-detection of data source, source label in output

Dependencies

Depends on PR #3 (comment support) for the IssueComment type.

Test plan

• Tested Dolt path against real beads data (37 issues, 8 comments migrated)
• Tested JSONL path against exported data (37 issues, 8 comments migrated)
• Cross-checked issue counts against beads (15 open, 22 closed match exactly)
• Full test suite passes (209 tests, 0 failures)
• Lint and typecheck clean

[jayminwest]

Thanks for tackling the Dolt migration path! The auto-detection fallback (JSONL -> Dolt -> error) is a clean design. A few things to sort out:

Must fix:

1. Overlapping commits with PR feat: add comment support (sd comment add/list/delete) #3 -- This PR includes the full comment feature as its first commit, which duplicates PR feat: add comment support (sd comment add/list/delete) #3. Please rebase so this PR only contains the migration/Dolt changes and targets the branch from PR feat: add comment support (sd comment add/list/delete) #3 (or main after feat: add comment support (sd comment add/list/delete) #3 merges). We'll merge feat: add comment support (sd comment add/list/delete) #3 first.

2. Wrap bd output parsing in try/catch (migrate.ts:95-106) -- JSON.parse on bd list --json output will throw an unhelpful error if the output is malformed or if bd doesn't support --json. Add a try/catch with a descriptive message like "Failed to parse bd list output. Is your bd CLI up to date?"

3. Validate issue IDs from bd before passing to Bun.spawn (migrate.ts:114-127) -- The IDs come from external CLI output. A quick regex check (e.g., confirm they match an expected ID pattern) before passing them as subprocess arguments would be good defensive practice.

Nice to have (non-blocking):

• The Dolt migration path has no automated tests. Even a basic test with a mock bd script returning known JSON would catch regressions.
• bd show calls are sequential per issue. For large installations this could be slow. Consider Promise.all with a concurrency limit as a follow-up.

[greghughespdx]

Will watch for PR #3 merge and then complete rebase for #4.