P1: model layer (convar->config inversion) + llmmeta

Lifts mort's pkg/logic/llms into executus/model, decoupled from mort:

- tiers.go: the tier resolver now reads a host-supplied config.Source under
  "model.tier.<name>" with host-supplied fallbacks (Configure(cfg, defaults,
  ttl)), instead of convar.Manager. Tier NAMES + specs are host config; the
  resolution mechanism (cache, reasoning-suffix dialect, chain validation) is
  generic. No tier names hard-coded in the harness.
- sink.go: usage/trace recording inverted off mort's llmusage/llmtrace into
  UsageSink / TraceSink seams + a model-owned Span, with nil-safe context
  attribution helpers (WithModel/WithTraceID/WithUsageTool/WithUsageUser).
  Both sinks optional (nil = off) so a light host records nothing.
- lane decoration repointed to executus/lane; utils.Errorf -> fmt.Errorf.
- call.go keeps GenerateWith[T] (instrumented structured output) — this is the
  structured-output primitive; no separate structured/ package.
- llmmeta moved over model/ (the meta-LLM helper: tier allowlist + JSON retry
  + ledger). Its tests configure a minimal tier table via TestMain.

New tests cover the inversion: config overrides fallback, tier registration,
reasoning-suffix survival, nested-tier rejection, nil-sink no-ops.

Full module: go build/vet/test -race green; core go.sum still free of
gorm/redis/discordgo/sqlite.

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

CLAUDE.md

@@ -48,11 +48,12 @@ CORE (majordomo + stdlib):
   dispatchguard/  loop/depth/fan-out caps                [P0 ✓]
   pendingattach/  attachment dedupe                      [P0 ✓]
   tool/     registry + 3-stage permissions + ssrf        [P1 ✓]
-  model/    config-driven tier resolution over majordomo [P1]
-  llmmeta/  shared meta-LLM helper (moves with model/)    [P1]
+  model/    config-driven tier resolution over majordomo [P1 ✓]
+            (convar->config.Source; UsageSink/TraceSink seams; GenerateWith[T]
+             structured output — no separate structured/ pkg)
+  llmmeta/  shared meta-LLM helper over model/            [P1 ✓]
   compact/  context compactor (WithCompactor hook)       [P2]
   tools/{web,net,store,compose,meta,comms}  generic tools [P3]
-  structured/  Generate[T] convenience over majordomo    [P1]
 
 BATTERIES (opt-in siblings, each nil-safe + a default):
   persona/   Agent noun + AgentStore seam + yml loader   [P4]