Fix deprecated API lint findings

[williammartin]

Description

Fixes the 4 golangci-lint findings on trunk, which all come from deprecated standard library APIs:

• reflect.Ptr → reflect.Pointer in pkg/x/markdown/accessibility_test.go.
• http.Transport.Dial/DialTLS → DialContext/DialTLSContext in pkg/api/http_client.go.

The second fix changes the transport go-gh uses when http_unix_socket is configured. In that setup, every request goes to a local unix socket instead of the network. No test covered this, so I added two tests, one for each dialer. Each starts a small HTTP server on a unix socket and requests a URL whose host can't resolve, so a response can only come from that server. One test requests an http:// URL, which uses DialContext. The other requests an https:// URL, which uses DialTLSContext and must reach the socket as plain HTTP.

How did you test this change?

I ran golangci-lint run ./... and saw the 4 findings before the change and 0 issues. after it. The new tests pass both before and after the fix. When I removed DialContext, only the http:// test failed. When I removed DialTLSContext, only the https:// test failed.

Key points

The tests put their sockets in os.MkdirTemp instead of t.TempDir(), because macOS limits socket paths to 104 bytes and the t.TempDir() path is longer.

Notes for reviewers

CI lints with golangci-lint v2.6.0, which may not report these findings. I found them with v2.14.0.

Authorship and follow-up

Who wrote this:

• A human wrote it.
• An agent wrote it under close human direction.
• An agent wrote it independently, and no human has guided the implementation beyond the initial prompt.

Who answers review comments:

• @williammartin will read and reply directly.
• An agent will draft replies and @williammartin will read them before they are posted.
• Nobody has explicitly committed to replying.

[Copilot]

🟢 Approval recommended

The focused API migrations preserve intended behavior and are adequately covered by the new transport test.

0 open findings

What changed in this PR

Updates deprecated Go APIs while preserving Unix-domain socket transport behavior.

Changes:

• Replaces deprecated reflection constants.
• Migrates HTTP transport dialers to context-aware APIs.
• Adds HTTP/HTTPS Unix socket coverage.

File	Description
pkg/​x/​markdown/​accessibility_test.go	Uses reflect.Pointer.
pkg/​api/​http_client.go	Uses context-aware socket dialers.
pkg/​api/​http_client_test.go	Tests Unix socket routing.

🧠 Review effort: Balanced

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