NNTP shares: the account's connections shared by priority

The coordinator (38) and the prober (8) had a fixed split; with history
paused the coordinator's stood idle while the prober's were its limit.
nntp_shares: each process syncs every 15 s (priority, minimum, what it could
use, what it has open) and gets what it may open: minimums first, then by
priority what each wants, growing only into connections the others closed
or gave up. The pool's size and the prober's lanes follow the grant; the
coordinator doubles its want while work waits for a connection, else asks
for its peak in use and a margin; the prober wants its maximum unless the
queue is dry. Claims scale with the lanes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

start/env.ts

@@ -43,6 +43,9 @@ export default await Env.create(new URL('../', import.meta.url), {
   NNTP_PASSWORD: Env.schema.string.optional(),
   NNTP_SECURE: Env.schema.boolean.optional(),
   NNTP_CONNECTIONS: Env.schema.number.optional(),
+  NNTP_MIN_CONNECTIONS: Env.schema.number.optional(),
+  NNTP_ACCOUNT_CONNECTIONS: Env.schema.number.optional(),
+  NNTP_RESERVED_CONNECTIONS: Env.schema.number.optional(),
   NNTP_TIMEOUT_MS: Env.schema.number.optional(),
   NNTP_HEDGE_AFTER_SECONDS: Env.schema.number.optional(),
   NNTP_HEDGE_CONNECTIONS: Env.schema.number.optional(),
@@ -74,6 +77,7 @@ export default await Env.create(new URL('../', import.meta.url), {
   SPOOL_MAX_GB: Env.schema.number.optional(),
   PREFETCH_PER_RANGE: Env.schema.number.optional(),
   PROBE_CONNECTIONS: Env.schema.number.optional(),
+  PROBE_MIN_CONNECTIONS: Env.schema.number.optional(),
   HTTP_ROUTES: Env.schema.enum.optional(['all', 'node', 'public'] as const),
   PREFETCH_PER_GROUP: Env.schema.number.optional(),
 })