Centralize error handling patterns in storage layer (bd-bwk2)

Created internal/storage/sqlite/errors.go with:
- Sentinel errors: ErrNotFound, ErrInvalidID, ErrConflict, ErrCycle
- wrapDBError helpers that auto-convert sql.ErrNoRows to ErrNotFound
- Type-safe error checking with errors.Is() compatibility

Updated error handling across storage layer:
- dirty.go: Added context to error returns, converted sql.ErrNoRows checks
- util.go: Updated withTx to use wrapDBError
- batch_ops.go: Added context wrapping to batch operations
- dependencies.go: Wrapped errors from markIssuesDirtyTx calls
- ids.go: Added error wrapping for ID validation

Also restored sqlite.go that was accidentally deleted in previous commit.

All tests pass. Provides consistent error wrapping with operation context
for better debugging.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/storage/sqlite/ids.go

@@ -205,7 +205,7 @@ func EnsureIDs(ctx context.Context, conn *sql.Conn, prefix string, issues []*typ
 		if issues[i].ID != "" {
 			// Validate that explicitly provided ID matches the configured prefix (bd-177)
 			if err := ValidateIssueIDPrefix(issues[i].ID, prefix); err != nil {
-				return err
+				return wrapDBErrorf(err, "validate ID prefix for %s", issues[i].ID)
 			}
 			
 			// For hierarchical IDs (bd-a3f8e9.1), ensure parent exists