ckpool: expose bestever in runtime socket JSON

Upstream ckpool tracks user/worker best_ever across block solves but
only emits it in the on-disk users.json/workers.json persistence files,
not in the runtime socket API (userinfo() / workerinfo() in
stratifier.c). Consumers that poll the socket — like kamado-api — see
bestdiff reset to zero on every block solve via reset_bestshares()
with no all-time field to fall back on. That is the "best share stuck
at zero after a block" UX we want to fix in Kamado.

0001-expose-bestever-in-runtime-json.patch adds bestever to the two
JSON_CPACK calls so the UI can show current-round and all-time side
by side. No behavioral change, no impact on share validation or block
handling. Candidate for upstreaming.

Also surfaces BestEver in api/internal/ckpool types (User, Worker).
Gracefully degrades to 0 on an unpatched ckpool.

api/internal/ckpool/types.go

@@ -35,12 +35,15 @@ type PoolStats struct {
 	DSPS10080    float64 `json:"dsps10080"`
 }
 
-// User is one entry in the `users` response.
+// User is one entry in the `users` response. BestEver is exposed by the
+// Kamado ckpool patch (patches/0001-expose-bestever-in-runtime-json.patch)
+// and will be 0 against an unpatched upstream ckpool.
 type User struct {
 	User      string  `json:"user"`
 	ID        int64   `json:"id"`
 	Workers   int     `json:"workers"`
 	BestDiff  float64 `json:"bestdiff"`
+	BestEver  float64 `json:"bestever"`
 	DSPS1     float64 `json:"dsps1"`
 	DSPS5     float64 `json:"dsps5"`
 	DSPS60    float64 `json:"dsps60"`
@@ -53,7 +56,8 @@ type UsersResponse struct {
 	Users []User `json:"users"`
 }
 
-// Worker is one entry in the `workers` response.
+// Worker is one entry in the `workers` response. BestEver requires the
+// Kamado ckpool patch; see User above.
 type Worker struct {
 	User      string  `json:"user"`
 	Worker    string  `json:"worker"`
@@ -64,6 +68,7 @@ type Worker struct {
 	DSPS1440  float64 `json:"dsps1440"`
 	LastShare int64   `json:"lastshare"`
 	BestDiff  float64 `json:"bestdiff"`
+	BestEver  float64 `json:"bestever"`
 	MinDiff   float64 `json:"mindiff"`
 	Idle      bool    `json:"idle"`
 }