fix(ingestion): confine /ingest-path and brain_ingest paths to brain/raw/

Both read a caller-chosen server path with extract.Text, so any file the
pod could read (the ServiceAccount token, /etc/passwd) could be ingested
into the brain and read back with brain_query.

ResolveIngestPath resolves relative paths against brain/raw/ (the inbox
the watcher already owns), evaluates symlinks, and refuses anything
that lands outside. A directory ingest re-resolves every walked file,
so a symlinked file inside raw/ cannot lead out. Existing ingest-path
tests moved their fixtures under brain/raw/.

Refs #149

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

ingestion/internal/mcp/handlers.go

@@ -543,6 +543,12 @@ func (s *Server) brainIngest(ctx context.Context, args json.RawMessage) (json.Ra
 	}
 
 	if a.Path != "" {
+		// Confined to brain/raw/ with symlinks evaluated (hyperguild#149).
+		resolved, err := api.ResolveIngestPath(s.brainDir, a.Path)
+		if err != nil {
+			return nil, err
+		}
+		a.Path = resolved
 		text, err := extract.Text(a.Path)
 		if err != nil {
 			return nil, fmt.Errorf("extract: %w", err)