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/obsidian.go

@@ -84,13 +84,14 @@ func (o *ObsidianIngester) ingestNote(path, vault string) (*IngestResult, error)
 		modified = created
 	}
 
-	// Fingerprint by content (so edits create updates)
+	// Fingerprint by content + relative vault path (machine-independent):
+	// the same note on two hosts maps to the same fingerprint.
+	relPath, _ := filepath.Rel(vault, path)
 	fp := FingerprintWithMeta(data, map[string]string{
 		"source": "obsidian",
-		"path":   path,
+		"path":   relPath,
 	})
 
-	relPath, _ := filepath.Rel(vault, path)
 	summary := extractBodyPreview(content, 200)
 
 	return &IngestResult{