fix(pipeline,api): write the source page last; say how to clear an unreadable note (review of #211, pass 4)

The source page carries source_hash, which the drift check trusts. Written first,
a batch that failed midway left a hash behind, so re-ingesting the same content
was skipped and the rest of the batch was lost for good. In a wing it is now
written last. An over-cap note in brain_pending says promote/reject cannot act
on it and to delete or move it by hand. Mutation-checked.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ingestion/internal/pipeline/pipeline.go

@@ -11,6 +11,7 @@ import (
 	"github.com/mathiasbq/hyperguild/ingestion/internal/brainfs"
 	"io/fs"
 	"path/filepath"
+	"sort"
 	"strings"
 	"time"
 
@@ -166,6 +167,12 @@ func buildAndWrite(ctx context.Context, wing string, rawPages []RawPage, sourceS
 		warnings = append(warnings, clashWarnings...)
 	}
 
+	if wing != "" {
+		// The source page carries source_hash, which the drift check trusts: it
+		// goes last, so a batch that fails midway leaves nothing to hide behind.
+		sort.SliceStable(merged, func(i, j int) bool { return !isSourcePath(merged[i].Path) && isSourcePath(merged[j].Path) })
+	}
+
 	var written []string
 	for _, page := range merged {
 		if !dryRun {