fix(ingestion): every brain/raw/ reader goes through an os.Root; symlinks are inert

raw/ is writable via Syncthing (a sendreceive folder shared with
flamingo, symlinks synced) and by the brain CronJobs, and several
readers followed symlinks out of it:

- /pending and brain_pending showed a symlink target's contents;
  brain_promote would copy it into wiki/ (then brain-sync to Gitea);
  brain_reject would copy it into raw/rejected/.
- The watcher, which needs no API call at all, ingested symlinked files
  (WalkDir yields them; extract.Text followed them). Not in the issue;
  found while fixing it.
- Ingest checked a path then reopened it by name (TOCTOU).

OpenRawRoot opens brain/raw as an os.Root and refuses a raw/ that is
itself a symlink. ListPending, PromoteNote and RejectNote read through
it and refuse anything not a regular file. extract.TextIn reads through
a root (temp copy for pdf/docmark); /ingest-path, brain_ingest and the
watcher use it, and the watcher archives via the root too, so a file
swapped for a symlink after a check still cannot lead out.

Refs #153

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

ingestion/internal/mcp/handlers.go

@@ -12,7 +12,6 @@ import (
 	"github.com/mathiasbq/hyperguild/ingestion/internal/api"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/capture"
-	"github.com/mathiasbq/hyperguild/ingestion/internal/extract"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/graphsync"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/notes"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/pipeline"
@@ -549,7 +548,7 @@ func (s *Server) brainIngest(ctx context.Context, args json.RawMessage) (json.Ra
 			return nil, err
 		}
 		a.Path = resolved
-		text, err := extract.Text(a.Path)
+		text, err := api.ReadIngestFile(s.brainDir, a.Path)
 		if err != nil {
 			return nil, fmt.Errorf("extract: %w", err)
 		}