fix: use timeout-bounded HTTP client for unary Read and Append (#255)

closes #234 

## Summary
- Unary `Read` and `Append` were using `getHTTPClient()` which returns
the streaming HTTP client (`Timeout: 0`), ignoring the configured
`RequestTimeout`.
- Changed both to use `s.basinClient.httpClient` (the timeout-bounded
client), consistent with `CheckTail` and other unary operations.
- Streaming sessions (`AppendSession`, `ReadSession`) continue to use
the no-timeout streaming client via `getHTTPClient()`.

## Test plan
- [ ] Verify `go build ./...` passes
- [ ] Confirm unary `Read`/`Append` now respect `RequestTimeout` under
network delays

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: infiniteregrets

s2/append.go

@@ -40,7 +40,7 @@ func (s *StreamClient) Append(ctx context.Context, input *AppendInput) (*AppendA
 	pbInput := convertAppendInputToProto(prepared)
 
 	httpClient := &httpClient{
-		client:      s.getHTTPClient(),
+		client:      s.basinClient.httpClient,
 		baseURL:     s.basinClient.baseURL,
 		accessToken: s.basinClient.accessToken,
 		logger:      s.logger,

s2/read.go

@@ -97,7 +97,7 @@ func (s *StreamClient) Read(ctx context.Context, opts *ReadOptions) (*ReadBatch,
 
 	batch, err := withRetries(ctx, s.basinClient.retryConfig, s.logger, func() (*ReadBatch, error) {
 		httpClient := &httpClient{
-			client:      s.getHTTPClient(),
+			client:      s.basinClient.httpClient,
 			baseURL:     s.basinClient.baseURL,
 			accessToken: s.basinClient.accessToken,
 			logger:      s.logger,