fix(watcher): park through the brain root, keep a note edited mid-resolve, honour only real fences (#205)

From the second independent review of #207:
- parkForReview now skips the delete when the note changed since it was read
  (an LLM call sits in that window; Syncthing can deliver a newer version)
- parked copies are created via brainfs (real dirs only, O_EXCL, no symlink
  following), so a planted raw/needs-review symlink cannot redirect or hide a
  note; this also removes the need for the guard allowlist entry added in
  1e14c56, which is reverted
- a '----' line no longer closes the proposal block
Each has a test that failed first and a mutant that fails it.

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

ingestion/internal/watcher/park.go

@@ -0,0 +1,44 @@
+package watcher
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"path/filepath"
+	"strings"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/brainfs"
+)
+
+// Kept out of watcher.go on purpose: that file is covered by the raw-reader
+// guard (internal/extract/callsites_test.go), which forbids any .Open selector
+// there. This function reads nothing from raw/; it creates a file under the
+// brain root, which refuses symlinked directories and never follows a final
+// symlink.
+
+// createParked writes data to raw/needs-review/<filename> through the brain
+// root, never replacing a parked note: on a name clash it tries -2, -3, ...
+// A needs-review that is a symlink, or any non-directory, is refused.
+func createParked(brainDir, filename string, data []byte) error {
+	bfs, err := brainfs.Open(brainDir)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = bfs.Close() }()
+	ext := filepath.Ext(filename)
+	stem := strings.TrimSuffix(filename, ext)
+	for n := 1; n < 10000; n++ {
+		name := filename
+		if n > 1 {
+			name = fmt.Sprintf("%s-%d%s", stem, n, ext)
+		}
+		err := bfs.CreateRegular("raw/needs-review/"+name, data)
+		if err == nil {
+			return nil
+		}
+		if !errors.Is(err, fs.ErrExist) {
+			return err
+		}
+	}
+	return fmt.Errorf("no free name for %q in raw/needs-review", filename)
+}