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.

README.md

@@ -483,9 +483,10 @@ cached bodies for the same request.
 - **Group override**: `GroupConfig.cache` (a `*bool`) overrides the
   top-level `cache.enabled` setting per group — `nil` inherits it, `false`
   opts the group out even when caching is globally on, `true` opts the
-  group in. Setting `true` on a group when the top-level `cache` block is
-  absent entirely is a construction error: there is nothing configured to
-  inherit `ttl`/`maxBodyBytes` from.
+  group in. Setting `true` on a group when the top-level `cache` is not
+  enabled — the block omitted entirely, or present with `enabled: false`,
+  both read the same way — is a construction error: there is nothing
+  configured to inherit `ttl`/`maxBodyBytes` from.
 - **Storage**: values are stored via the same hand-rolled RESP2 client
   (`resp.go`) the limiter's distributed counters use — the identical
   Redis/Valkey/Dragonfly connection, not a second one. A Redis error
@@ -575,7 +576,8 @@ request to any of them falls through to the plugin's existing
   themselves.
 - **`GET /admin`** serves the dashboard's HTML/CSS/JS shell. This route is
   deliberately served **with no authentication at all** once
-  `admin.enabled` is true (disabled still 404s): a browser navigating
+  `admin.enabled` is true (disabled still falls through to the same
+  404/`passthroughUnknown` handling described above): a browser navigating
   straight to the URL has no way to attach a custom `Authorization` or
   `x-api-key` header, so gating the page itself would make it unreachable
   from a browser in the first place. This is safe because the shell