fix(pipeline,classification): read the brain through brainfs (#157, slice 6) (#176)

Ingest pipeline readers (readSourcePage and loadSchema feed the LLM prompt; reviseOrCreate; injectSourceRefs; BackfillRefs list and reads) and classification.Load read through brainfs: symlinked or special files no longer reach the prompt, written pages or the I1 sovereignty config, and a FIFO no longer hangs ingest or startup. A symlinked/special classification.yaml is a hard error; an absent one still yields defaults.

Refs #157. Adversarial review: BLOCKED, BLOCKED, PASS. Follow-ups: #158 (write paths), #179 (FIFO tripwire).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Mathias <mthbqv@gmail.com>

ingestion/internal/pipeline/refs.go

@@ -2,7 +2,6 @@
 package pipeline
 
 import (
-	"os"
 	"path/filepath"
 	"regexp"
 	"strings"
@@ -53,8 +52,7 @@ func injectSourceRefs(pages []wiki.Page, inventory map[wiki.PageType][]wiki.Entr
 		if !ok {
 			continue
 		}
-		diskPath := filepath.Join(brainDir, "wiki", string(pt), slug+".md")
-		b, err := os.ReadFile(diskPath)
+		b, err := readBrainFile(brainDir, "wiki/"+string(pt)+"/"+slug+".md")
 		if err != nil {
 			continue
 		}