feat: Add batch deletion support (bd-127)

- Add DeleteIssues() method in sqlite.go for atomic batch deletion
- Support multiple issue IDs as arguments or from file
- Add --from-file flag to read IDs from file (supports comments)
- Add --dry-run mode for safe preview without deleting
- Add --cascade flag for recursive deletion of dependents
- Add --force flag to orphan dependents instead of failing
- Pre-collect connected issues before deletion for text reference updates
- Add orphan deduplication to prevent duplicate IDs
- Add rows.Err() checks in all row iteration loops
- Full transaction safety - all deletions succeed or none do
- Comprehensive statistics tracking (deleted, dependencies, labels, events)
- Update README and CHANGELOG with batch deletion docs

Fixed critical code review issues:
- Dry-run mode now properly uses dryRun parameter instead of deleting data
- Text references are pre-collected before deletion so they update correctly
- Added orphan deduplication and error checks
- Updated defer rollback pattern per Go best practices

README.md

@@ -315,6 +315,58 @@ bd update bd-1 --status in_progress --json
 bd close bd-1 --json
 ```
 
+### Deleting Issues
+
+Delete one or more issues, with automatic cleanup of references and dependencies:
+
+```bash
+# Single issue deletion (preview mode)
+bd delete bd-1
+
+# Force single deletion
+bd delete bd-1 --force
+
+# Batch deletion
+bd delete bd-1 bd-2 bd-3 --force
+
+# Delete from file (one ID per line, supports # comments)
+bd delete --from-file deletions.txt --force
+
+# Dry-run mode (preview without changes)
+bd delete --from-file deletions.txt --dry-run
+
+# Cascade deletion (recursively delete dependents)
+bd delete bd-1 --cascade --force
+
+# Force deletion (orphan dependents instead of failing)
+bd delete bd-1 --force
+
+# JSON output
+bd delete bd-1 bd-2 --force --json
+```
+
+The delete operation:
+- Removes all dependency links (both directions)
+- Updates text references to `[deleted:ID]` in connected issues
+- Deletes the issue from database and JSONL
+- Atomic: all deletions succeed or none do
+
+**Dependency handling:**
+- **Default**: Fails if any issue has dependents not in deletion set
+- **`--cascade`**: Recursively deletes all dependent issues
+- **`--force`**: Deletes and orphans dependents (use with caution)
+
+**File format** for `--from-file`:
+```text
+# Cleanup test issues
+bd-100
+bd-101
+bd-102
+
+# Another batch
+bd-200
+```
+
 ### Renaming Prefix
 
 Change the issue prefix for all issues in your database. This is useful if your prefix is too long or you want to standardize naming.