Stage M-0: kernel-Hermes arena, pending queues and member lists grow on demand; Q_SLOT its own constant (FABRIC-3.9.0 §7.0, M-0/M-0b)

- The static sk_hermes_msgs[32] is replaced by a directory of fixed-size
  segments (SK_HERMES_ARENA_SEGMENT, growth granularity only). Messages
  never move -- callers, including the drain across vm_interpret_kind(),
  hold message pointers across later allocations, so copy-on-grow (as
  §7.0 first proposed) would dangle them. Each message carries its index;
  numbering unchanged.
- Pending-queue rings and channel member lists heap-grown (doubling);
  member lists freed on destroy; reassembly scratch sized per call.
  SK_HERMES_MSG_MAX / _PENDING_MAX / _MEMBER_MAX are gone.
- Q_SLOT = Q48_ONE / 32 as its own constant (M-0b), value unchanged.
- Every grow failure is printed, logged at LOG_ERROR, counted
  (sk_hermes_grow_failures()) and refused whole; a send whose queue can't
  grow releases its message.

Probe (reverted), identical on amd64/aarch64/riscv64: 70 messages in one
queue (arena 32 -> 96), sender refused by its reservoir, 72 popped intact
in order, 100 members; a live Hera drain on a full arena grew it mid-drain
and released/popped the right message; each grow path's injected failure
refused whole and counted. 3-ISA acceptance passes; boot parity, dict_hash
set and the live ledger line byte-identical to before.

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

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