Pre-migration the spans started from context.Background(), so storage
errors were always real internal failures. Post-migration the request
ctx flows through; when a client cancels or hits its deadline mid-call,
storage backends return context.Canceled / context.DeadlineExceeded.
Wrapping those as CodeInternal told clients "server bug" when in fact
the truth is "your request was cancelled/timed out".

internalErr() inspects the storage error and picks the right code:
- context.Canceled         -> CodeCanceled
- context.DeadlineExceeded -> CodeDeadlineExceeded
- otherwise                -> CodeInternal

Applied across all 8 internal-error sites in Has/Set/MGet/MExpire/TTL/
Delete/Clear.

Also: tests/kv_plugin_test.go h2c Dialer gets a 30s Timeout so the
suite can't hang on a TCP connect stall if the rpc server is down.
Request body remains unbounded.

Resolves coderabbitai + Copilot threads on PR #119.

Per user preference: Connect handler bodies pull each field directly
from req.Msg, no local alias. Keeps the call site self-documenting.

New tests/kv_api_test.go (with a minimal in-memory config) verifies that
the same kv handler mounted on the rpc plugin serves both wire formats:

- TestKVHTTPApi: Connect-RPC over h2c, the protocol PHP clients use.
- TestKVGRPCApi: regular gRPC (google.golang.org/grpc) on the same port.

Both run a Set / Has / Delete / Has cycle and assert state changes
end-to-end. The shared startKvAPIContainer helper brings up rpc + kv +
memory + logger, so the suite stays Docker-free.

The kv handler is mounted once on the rpc plugin's mux but Connect-RPC
hands it three wire protocols out of the box. This commit adds one
test per protocol against the same in-memory storage, all running a
Set / Has / Delete / Has cycle:

- TestKVConnectAPI: Connect over h2c via connectrpc.com/connect.
- TestKVHTTPApi:    plain HTTP/1.1 POST with a protojson body and
  Content-Type: application/json. This is the shape PHP clients use
  (no Connect SDK; Guzzle/curl + json_encode).
- TestKVGRPCApi:    regular gRPC via google.golang.org/grpc + the
  gRPC-generated client. Used by PHP's gRPC extension.

Helper startKvAPIContainer brings up rpc + kv + memory + logger.

api-go v6.0.0-beta.6 (tagged off api PR #71) re-generates the
KvServiceHandler with WithIdempotency(IdempotencyNoSideEffects) on
Has / MGet / TTL. Connect now accepts HTTP GET on those, encoding the
request body in query params.

- Bump api-go: v6.0.0-beta.5 -> v6.0.0-beta.6 in root + tests modules.
- Replace the temporary TestKVHTTPGetRejected probe with a table-driven
  TestKVHTTPGetIdempotency that asserts:
    GET Has, MGet, TTL              -> 200 OK
    GET Set, MExpire, Delete, Clear -> 405 Method Not Allowed
  Provides regression coverage for the proto idempotency annotations.

schema.json's pattern allows only `driver` + optional `config` keys per
storage, with strict additionalProperties=false on each driver's config.
The kv-init/api configs had drifted:

- `default` / `in-memory` (memory): the memory driver's KvFromConfig
  ignores its argument outright, and the schema's `memory` branch
  requires `config: {}` (empty object). The configs had `interval: 60`
  — silently dropped at runtime, invalid by schema. Replace with `{}`.
- `boltdb-south` / `boltdb-africa` (boltdb): boltkv.Config exposes only
  `file`, `permissions`, `interval` via mapstructure. The configs had
  `dir: "."` (no such field) and `bucket: "rr"` (private, hardcoded to
  "default"). Both were silently swallowed; drop them.
- memcached entry was already valid; left alone.

No runtime behavior change. JSON Schema validators (IDE / CI tooling)
now accept the configs cleanly.

`.rr-kv-bolt-no-interval.yaml` and `.rr-kv-bolt-perms.yaml` already
matched the schema and are unchanged.