feat(cli): mcpctl trace <code>, and bound the table it reads

The trace codes are now emitted in every deadline message and degradation
notice, so they need somewhere to go.

`mcpctl trace <code>` queries the audit events mcpd already stores and renders
the request as a waterfall: each step with its offset, duration, byte delta,
and any ⚠ degradation or ✗ error, then a summary naming the slowest step. No
new endpoint was needed -- GET /api/v1/audit/events?correlationId= already
existed and correlationId is already an indexed column; it just had nothing
writing meaningful values into it until this branch, and nothing reading it.

--strict exits non-zero when the trace contains an error or a degraded step, so
it composes into scripts. An empty result explains itself rather than printing
nothing: batches flush up to 5s late, old requests predate trace codes, and the
codes exclude I/L/O/U so a mistyped one is worth calling out.

Retention: AuditEvent had no prune at all. That was defensible while the table
was write-only; it is not now that a command reads it. Mirrors the AuditLog
convention exactly -- POST /api/v1/audit/events/purge, triggered rather than
scheduled, guarded by the existing audit-purge RBAC operation so it cannot be
granted by accident separately from the log purge. 30 days by default rather
than AuditLog's 90: these are several rows per MCP call, not a record of
administrative mutations.

Note for the plan's sake: I had assumed AuditLog retention was a scheduled job
registered in main.ts. It is not -- it is a manual endpoint. Mirroring what the
codebase actually does beat inventing a scheduler that exists for neither table.

completions are generated, so `trace` is registered in PROJECT_SCOPED_COMMANDS
and both shells regenerated; the freshness test passes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GqMidYEGUJG5fxeoTELBu2

completions/mcpctl.bash

@@ -5,8 +5,8 @@ _mcpctl() {
   local cur prev words cword
   _init_completion || return
 
-  local commands="status statusline 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 favourites"
+  local commands="status statusline login logout config get describe delete logs create edit apply chat chat-llm patch passwd errors trace backup approve review skills console cache provider test migrate rotate"
+  local project_commands="get describe delete logs create edit trace attach-server detach-server favourites"
   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"
   local resource_aliases="servers instances secrets secretbackends llms agents personalities templates projects users groups rbac prompts promptrequests serverattachments proxymodels inference-tasks all server srv instance inst secret sec secretbackend sb llm agent personality template tpl project proj user group rbac-definition rbac-binding prompt promptrequest pr serverattachment sa proxymodel pm task tasks inference-task"
@@ -289,6 +289,9 @@ _mcpctl() {
     errors)
       COMPREPLY=($(compgen -W "-n --limit -h --help" -- "$cur"))
       return ;;
+    trace)
+      COMPREPLY=($(compgen -W "-o --output --strict -h --help" -- "$cur"))
+      return ;;
     backup)
       local backup_sub=$(_mcpctl_get_subcmd $subcmd_pos)
       if [[ -z "$backup_sub" ]]; then