Fix issue-prefix config fallback to config.yaml (GH#1145) (#1146)

The config.yaml file uses "issue-prefix" (with hyphen) but this setting
was only read during bd init. After initialization, all code read from
the database's "issue_prefix" key, so subsequent changes to config.yaml
were silently ignored.

This fix adds a fallback to config.yaml's "issue-prefix" in the key
locations where the prefix is retrieved from the database:

1. autoflush.go: Auto-import now checks config.yaml before falling back
   to auto-detection from JSONL or directory name

2. autoflush.go: filterByMultiRepoPrefix now checks config.yaml as fallback

3. create.go: Direct mode prefix validation now checks config.yaml as fallback

Priority order is preserved:
1. Database issue_prefix (if set)
2. Config.yaml issue-prefix (new fallback)
3. Auto-detection from JSONL/directory (existing fallback)

Fixes #1145

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/create.go

@@ -432,8 +432,11 @@ var createCmd = &cobra.Command{
 				}
 				// If error, continue without validation (non-fatal)
 			} else {
-				// Direct mode - check config
+				// Direct mode - check config (GH#1145: fallback to config.yaml)
 				dbPrefix, _ = store.GetConfig(ctx, "issue_prefix")
+				if dbPrefix == "" {
+					dbPrefix = config.GetString("issue-prefix")
+				}
 				allowedPrefixes, _ = store.GetConfig(ctx, "allowed_prefixes")
 			}