Add tracing manifests and docs; clean up branch lint findings

Manager env block (downward-API resource attrs, commented OTLP
examples), architecture §10 + Decisions entries, README section.
Lint: goconst constants, gofmt, logcheck (Setup now takes its logger
from ctx via logf.FromContext).

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

docs/plans-executions/2026-08-24-1025-otel-tracing.md

@@ -10,7 +10,7 @@ Plan: `docs/plans/2026-08-24-1025-otel-tracing.md`
 - [x] Step 6 — Discovery server
 - [x] Step 7 — GC + health
 - [x] Step 8 — GCP wire-log enrichment
-- [ ] Step 9 — Manifests + docs
+- [x] Step 9 — Manifests + docs
 
 ## Step 1 — Dependencies
 
@@ -155,3 +155,29 @@ before the elision pass (both values are well under the 1KiB threshold).
 The new `wirelog_test.go` covers the enrichment, that the JWT/token security
 filter still drops non-wire Debug records even with a span present, and that
 spanless records stay unchanged.
+
+## Step 9 — Manifests, docs, lint
+
+`config/manager/manager.yaml` gained the OTel env block (downward-API
+`POD_NAME`/`POD_NAMESPACE` deliberately listed *before*
+`OTEL_RESOURCE_ATTRIBUTES` — `$(VAR)` expansion only sees earlier vars),
+with the OTLP endpoint and sampler left as commented examples so deployments
+stay tracing-off by default. `docs/architecture.md` got "### 10. Tracing"
+plus five Decisions entries; README got a Tracing section.
+
+`make lint` surfaced 16 new-on-branch issues (checked with
+`golangci-lint run --new-from-rev main`; the other ~43 pre-date this work):
+
+- one gofmt slip, 13 goconst repeats — fixed with `env*`/`exporter*`
+  constants in `internal/tracing/tracing.go` shared by the tests;
+- two logcheck hits ("function takes both a context and a logger"):
+  `Setup` now reads its logger from ctx (`logf.FromContext`, caller seeds
+  via `logf.IntoContext` — the linter's sanctioned pattern), and
+  `ContextWithLogger` carries a justified `//nolint:logcheck`, since being
+  the IntoContext-analogue is its purpose.
+
+Worth noting: pre-existing lint debt (50 goconst etc. on `main`) was left
+untouched — `make lint` still fails overall; only branch-introduced issues
+were cleaned. The lint fixes changed `Setup`'s signature after Step 2/4 had
+landed, so those commits show the two-arg version; this commit is where it
+settles.