fix(platformvm): accrue P-chain validator uptime for a stable set (reward gate)

All 5 mainnet validators read uptime=0.0000 / connected=null even for peers
connected 24h+, so prefersCommit (block/executor/options.go) always saw
0% < threshold and withheld staking rewards (~165M LUX gate).

Root causes (four, all fixed):

1. StartTracking never existed/called. The custom uptimeTracker was created
   late (onReady) and never baselined validator records, so a long-running
   validator's stored upDuration stayed 0 and CalculateUptimePercentFrom
   returned 0/total = 0.
2. upDuration flushed only on Disconnect/Shutdown, so a continuously-connected
   validator's persisted uptime never grew.
3. service.go left `connected` hard-nil ("IsConnected no longer exists").
4. ROOT: VM.Connected never fired. network.Connected -> chainRouter.Connected
   only added to a connectedPeers set and logged; it never dispatched to chain
   handlers, and blockHandler.Connected was a no-op. So tracker.Connect was
   never called and the connected map was always empty — nothing to accrue.

Fix (faithful port of avalanchego snow/uptime.Manager semantics, luxfi pkgs):

- vms/platformvm/uptime_tracker.go: rewrite as a startedTracking-gated tracker.
  StartTracking/StopTracking/StartedTracking/IsConnected added; CalculateUptime
  folds the live connected session forward to now using the persisted
  lastUpdated (reconstructed from the second-granular uptime.State encoding), so
  a connected validator accrues uptime WITHOUT a Disconnect. Before tracking, a
  validator is assumed online since its last update (avalanchego baseline);
  after tracking, only genuine sessions accrue. Second-granular clock matches
  storage. CalculateUptimePercentFrom is the clean upDuration/(now-from) form,
  clamped to [0,1].
- vms/platformvm/vm.go: create+register the tracker at Initialize (so bootstrap
  Connect events are captured), StartTracking(primary validators) at onReady,
  StopTracking on re-bootstrap and Shutdown. Mirrors avalanchego's
  onNormalOperationsStarted lifecycle.
- vms/platformvm/service.go: populate `connected` via tracker.IsConnected.
- node/chain_router.go: chainRouter.Connected/Disconnected now dispatch to every
  registered chain handler (snapshot under lock, call outside).
- chains/manager.go: blockHandler forwards Connected/Disconnected to its chain's
  VM (engineVM) exactly once (dedup set), so the P-chain uptime tracker — and
  every VM's peer set — finally observes connectivity.

Consensus safety: prefersCommit is a per-node PREFERENCE feeding oracle-block
voting, not a deterministic value. Fixing the local uptime measurement (which
was uniformly 0) changes only which reward option each node prefers; consensus
still converges by preference voting. No staking/reward math changed.

Tests (vms/platformvm/uptime_tracker_test.go, -race green):
- TestUptimeTrackerLongRunningValidatorAccruesUptime: a 30-day validator reports
  ~100%. Uses only the shared Calculator API; run against the OLD tracker it
  returns 0.0 (FAIL — the exact mainnet symptom), against the fix 1.0 (PASS).
- Continuously-connected-climbs, StartTracking-baselines, flush-on-disconnect,
  never-connected-gets-zero, StopTracking-flushes, idempotent double-connect,
  dedup, concurrency. block/executor (reward gate) suite green.

Follow-on (NOT in this commit): devnet 5-node uptime-climb verification ->
gated release -> owner-gated one-at-a-time mainnet roll. No image built, no
deploy, no live validator touched.

Co-authored-by: Hanzo Dev <dev@hanzo.ai>

version/constants.go

@@ -77,7 +77,7 @@ var (
 const (
 	defaultMajor = 1
 	defaultMinor = 36
-	defaultPatch = 13
+	defaultPatch = 26
 )
 
 func init() {