feat: PDF extraction and fuzzy entity resolution

- New extract package: Text() dispatcher for .md/.txt passthrough and
  PDF extraction via pdftotext subprocess
- wiki.Entry gains Aliases []string, loaded from YAML frontmatter
- Fuzzy entity resolution in pipeline: normalizes titles (lowercase,
  strip articles, collapse hyphens) and matches proposed pages against
  existing inventory slugs and aliases to prevent proliferation
- Watcher and API handler now use extract.Text() instead of os.ReadFile
- Dockerfile: apk add poppler-utils in Alpine runtime stage

ingestion/internal/watcher/watcher.go

@@ -12,6 +12,7 @@ import (
 	"time"
 	"unicode"
 
+	"github.com/mathiasbq/hyperguild/ingestion/internal/extract"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/pipeline"
 )
 
@@ -99,12 +100,12 @@ func processFile(ctx context.Context, cfg Config, path, date string) error {
 	filename := filepath.Base(path)
 	source := deriveSource(filename)
 
-	content, err := os.ReadFile(path)
+	content, err := extract.Text(path)
 	if err != nil {
-		return fmt.Errorf("read file: %w", err)
+		return fmt.Errorf("extract text: %w", err)
 	}
 
-	_, runErr := pipeline.Run(ctx, cfg.Pipeline, cfg.BrainDir, string(content), source, false)
+	_, runErr := pipeline.Run(ctx, cfg.Pipeline, cfg.BrainDir, content, source, false)
 	if runErr != nil {
 		// Copy to failed/ and leave a .failed marker so we don't retry.
 		failedDir := filepath.Join(cfg.BrainDir, "raw", "failed")