feat: M1 determinism fixes for gossip

Refs #1

- F1: canonical fingerprints (git identity by remote URL, log by
  basename, obsidian by relative vault path) so identical facts get
  identical ids across machines
- F2: node_id (persisted in settings) + Hybrid Logical Clock in all
  observation "when" columns; removed time.Now() fact-time fallbacks
- F3: stable TF-IDF tie-break sort (score desc, term asc)
- F4: observations carry (node_id, hcl) locator; dedup ordered by hcl

internal/ingest/log.go

@@ -69,7 +69,7 @@ func (l *LogIngester) Ingest(path string) (*IngestResult, error) {
 	}
 
 	base := filepath.Base(path)
-	fp := Fingerprint([]byte(path))
+	fp := Fingerprint([]byte("log:" + base))
 	title := fmt.Sprintf("Log %s (%d lines)", base, totalLines)
 	createdAt := ""
 	if fi, err := os.Stat(path); err == nil {
@@ -99,7 +99,7 @@ func (l *LogIngester) Ingest(path string) (*IngestResult, error) {
 	return &IngestResult{
 		Fingerprint:     fp,
 		SourceID:        l.SourceID(),
-		SourcePath:      path,
+		SourcePath:      base,
 		ContentType:     ".log",
 		Title:           title,
 		Summary:         summary,