feat(errors): mcpd error-log ring buffer + 'mcpctl errors'

Operators can now see recent mcpd error/fatal logs without kubectl:
- mcpd tees level>=error pino records into an in-memory ring buffer
  (src/mcpd/src/services/error-log-buffer.ts; wired via pino.multistream in
  server.ts so stdout logging is unchanged). Captures structured errors incl.
  fatal kinds like BACKEND_TOKEN_DEAD.
- GET /api/v1/logs/errors?limit=N (RBAC: 'logs' operation).
- CLI: 'mcpctl errors [-n N]' renders TIME/LEVEL/DETAIL, most-recent-first.

Buffer unit tests (6); full suite 2223 passing. Needs a deploy to go live.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

completions/mcpctl.bash

@@ -5,7 +5,7 @@ _mcpctl() {
   local cur prev words cword
   _init_completion || return
 
-  local commands="status login logout config get describe delete logs create edit apply chat chat-llm patch passwd backup approve review skills console cache provider test migrate rotate"
+  local commands="status login logout config get describe delete logs create edit apply chat chat-llm patch passwd errors backup approve review skills console cache provider test migrate rotate"
   local project_commands="get describe delete logs create edit attach-server detach-server"
   local global_opts="-v --version --daemon-url --direct -p --project -h --help"
   local resources="servers instances secrets secretbackends llms agents personalities templates projects users groups rbac prompts promptrequests serverattachments proxymodels inference-tasks all"
@@ -271,6 +271,9 @@ _mcpctl() {
     passwd)
       COMPREPLY=($(compgen -W "-h --help" -- "$cur"))
       return ;;
+    errors)
+      COMPREPLY=($(compgen -W "-n --limit -h --help" -- "$cur"))
+      return ;;
     backup)
       local backup_sub=$(_mcpctl_get_subcmd $subcmd_pos)
       if [[ -z "$backup_sub" ]]; then