docs: v0.2 features

README, examples, and a comment update covering v0.2's four features:

- README: new Caching section (key semantics incl. requestedModel +
  endpoint, hit/miss header, count-requests-free-tokens, group override,
  redis-required) and Admin section (enable flag, admin:true users,
  browser key-entry flow, sessionStorage, what's exposed/redacted,
  poll-counts-against-quota, unauthenticated-shell). Retry and Image/audio
  sections already existed from T3/T4; left as-is. Config reference gains
  cache/admin rows at the top level, GroupConfig.cache, UserConfig.admin,
  and full CacheConfig/AdminConfig tables. Known limitations gains
  images/audio-not-cost-accounted and cache-shares-entries-across-users.
- examples/kubernetes.yaml: adds cache{enabled:true,ttl:5m} (this example
  already configures redis) and admin{enabled:false} with a comment on
  enabling it, plus an inline admin:true user gated behind that flag.
  Round-trips through New() cleanly (verified with a throwaway test).
- examples/docker-compose.yml: adds retry, cache (left disabled — this
  minimal demo runs no Redis), and admin (left disabled, with a comment
  on enabling it). Round-trips through New() cleanly (verified the same
  way).
- admin.go: pluginVersion's doc comment now says to keep it in sync with
  the release tag.

examples/kubernetes.yaml

@@ -86,6 +86,16 @@ spec:
             requestsPerDay: 500
       users:
         file: /secrets/llmgw-users/users.json
+        inline:
+          # Grants the admin dashboard (see the "admin" block above),
+          # which stays unreachable until admin.enabled is true. In a
+          # real deployment this key still belongs in a Secret via
+          # env:/file: the same as every other apiKey here — inline only
+          # to keep this one example self-contained.
+          - name: dashboard-admin
+            group: engineering
+            apiKey: "env:LLMGW_ADMIN_KEY"
+            admin: true
       redis:
         address: redis.shared-resources.svc:6379
         password: "env:REDIS_PASSWORD"
@@ -94,6 +104,19 @@ spec:
         enabled: true
         attempts: 2 # retries after the first try: 3 tries total
         backoff: 250ms
+      # Opt-in response cache for non-streaming chat/embeddings — see
+      # ../README.md#caching. Requires the redis block above; without it,
+      # this would silently stay disabled (one warning logged) rather than
+      # fail construction.
+      cache:
+        enabled: true
+        ttl: 5m
+      # Disabled here deliberately: flip to `enabled: true`, then flag at
+      # least one user `admin: true` (see the inline "dashboard-admin"
+      # user under users.inline below) to try the read-only dashboard at
+      # https://llm.example.com/admin — see ../README.md#admin.
+      admin:
+        enabled: false
       pricing:
         gpt-5-mini: {inputPerM: 0.25, outputPerM: 2.0}
       mcpServers: