fix(docs,integration): example env completeness, flaky reset, cache key assertion

Task 5 re-review fixes: 1 Important + 3 folded.

1. (Important) examples/kubernetes.yaml was construction-broken on
   copy-paste: the inline dashboard-admin user resolves env:LLMGW_ADMIN_KEY
   at construction time regardless of admin.enabled, but the Helm env
   snippet never listed it. Added it there, alongside a comment on the
   admin user explaining the env var is required either way. Fixed the
   two reversed above/below cross-references (kubernetes.yaml:90/:115)
   and reworded the misleading "self-contained" comment on the inline
   admin user. Verified with a throwaway round-trip test covering: no env
   vars set fails, every documented env var set succeeds (admin.enabled
   staying false as committed), and — the actual bug — every var set
   EXCEPT LLMGW_ADMIN_KEY still fails even with admin disabled.

2. README: Admin section's "(disabled still 404s)" now points at the
   same 404/passthroughUnknown wording the section already uses above it.
   Caching section's "block absent entirely is a construction error" now
   says "not enabled" — auth.go's actual check is !cfg.Cache.Enabled,
   which is identically true whether the block is omitted or present with
   enabled: false.

3. integration/mock/main.go: added POST /flaky/reset (handleFlakyReset),
   reachable through the "flaky" provider's own native passthrough route,
   resetting the atomic hit counter on demand. TestRetryFlakyRecovers now
   calls it at the start of the test, removing the make integration-keep
   re-run trap the old doc comment warned about instead of fixing.
   dynamic.yml.tmpl's stale "test 8" comment now reads "task 5".

4. integration_test.go: added redisKeys (docker compose exec redis-cli
   KEYS, mirroring flushRedis's own pattern) and a
   TestResponseCache assertion that redis holds at least one
   llmgw:cache:* key immediately after the miss request.

go test ./... -count=1, gofmt, vet, make yaegi-check all pass; make
integration exits 0 across two fresh full runs.

integration/traefik/dynamic.yml.tmpl

@@ -44,14 +44,16 @@ http:
               baseUrl: "http://mockgemini:8080"
               apiKey: "mock-gemini-key"
               models: ["gemini-mock"]
-            # Backs test 8's retry coverage only: baseUrl points at the
+            # Backs task 5's retry coverage only: baseUrl points at the
             # SAME mockopenai container, under its dedicated /flaky prefix
             # (see integration/mock/main.go's handleFlakyOpenAIChat), so
             # a.baseURL+"/v1/chat/completions" (provider_openai.go)
-            # resolves to /flaky/v1/chat/completions. discovery is left
-            # off — GET /flaky/v1/models isn't served — so the explicit
-            # "flaky-mock" model id below is the only way this provider's
-            # model is known.
+            # resolves to /flaky/v1/chat/completions, and this provider's
+            # own native passthrough route (/flaky/reset) reaches
+            # handleFlakyReset the same way. discovery is left off — GET
+            # /flaky/v1/models isn't served — so the explicit "flaky-mock"
+            # model id below is the only way this provider's model is
+            # known.
             flaky:
               type: openai
               baseUrl: "http://mockopenai:8080/flaky"