fix: derived-state determinism, error visibility, metrics naming, HTTP hardening

- rebuild: fold observations per fingerprint in a total order
  (hcl DESC, node_id DESC, id DESC) so two nodes with identical logs
  rebuild identical entries (was: arbitrary bare-column row, merge-order
  dependent)
- threads: CreateThreadCluster uses INSERT OR IGNORE + existing-id
  fallback — concurrent auto-threaders converge instead of hitting UNIQUE
- errors surfaced instead of swallowed: scanEntries returns rows.Err(),
  Stats() fails fast on query errors, AutoLinkThreadObservations /
  linkTemporalNeighbors / golden-thread linking propagate failures,
  AddThreadNote + LinkObservationToThread write under one tx,
  watch records session upsert failures
- gossip client: push checks HTTP status and reports errors (a broken
  push direction no longer looks like a silent success); gossip diff
  gets a 10s timeout so a dead peer cannot hang the CLI
- ingest: failed source sweeps (obsidian/browser/gitea) are logged,
  and -d's help text now states its file-only scope
- watch --quiet: fatal errors go to stderr instead of io.Discard
- main: cobra SilenceErrors/SilenceUsage (errors print once, usage is
  not dumped on runtime failures); knox mcp exits 0 on SIGINT/SIGTERM
- metrics: drop _total suffix from gauges (knox_observations,
  knox_entries, knox_projects, knox_sessions, knox_peers, knox_threads);
  _total stays on counters per Prometheus convention
- http: ReadHeaderTimeout + IdleTimeout on gossip, metrics, and web servers

tests: concurrent cluster-create idempotency, HCL-order rebuild fold
(both merge orders), push HTTP-error surfacing; full suite + -race pass,
gofmt clean

internal/watch/gossip.go

@@ -242,6 +242,9 @@ func (c *Client) Push(kdb *db.KnoxDB, peerVector map[string]int64) (int, error)
 		return 0, err
 	}
 	defer resp.Body.Close()
+	if resp.StatusCode/100 != 2 {
+		return 0, fmt.Errorf("push to %s: %s", c.Addr, resp.Status)
+	}
 	var out struct {
 		Accepted int `json:"accepted"`
 	}
@@ -354,7 +357,13 @@ func Run(kdb *db.KnoxDB, m *metrics.Metrics, static []string) int {
 			m.IncrementPull(pulled)
 		}
 
-		pushed, _ := c.Push(kdb, p.Vector)
+		pushed, err := c.Push(kdb, p.Vector)
+		if err != nil {
+			log.Printf("[gossip] push %s: %v", addr, err)
+			if m != nil {
+				m.IncrementErrors()
+			}
+		}
 		if m != nil {
 			m.IncrementPush(pushed)
 		}