fix(net): respect HTTP proxy environment variables

[krasserm]

Summary

• Add Proxy: http.ProxyFromEnvironment to all custom http.Transport and bare http.Client instances so that HTTP_PROXY, HTTPS_PROXY, and ALL_PROXY environment variables are honored
• Fixes DNS resolution failures (no such host) when running inside sandboxed environments that route traffic through HTTP/SOCKS proxies

Problem

A custom http.Transport{} defaults Proxy to nil, unlike http.DefaultTransport which uses http.ProxyFromEnvironment. The base transport in optionsForAccountScopes (and bare http.Client instances used for OAuth token exchanges) silently bypassed all proxy settings.

Changes

Seven locations fixed across four packages:

File	Context
internal/googleapi/client.go:128	Primary transport for all Google API calls
internal/googleapi/client.go:81	OAuth token refresh client
internal/googleapi/service_account.go:23	Service account token exchange
internal/googleauth/token_check.go:32	Refresh token validation
internal/googleauth/token_email.go:38	Email lookup from token
internal/googleauth/accounts_server.go:526	User info fetching
internal/cmd/gmail_watch_cmds.go:319	Webhook delivery client

Test plan

• New TestProxyEnvRespected verifies the full transport chain and OAuth client route through HTTP_PROXY
• All existing tests pass
• make lint and make fmt-check pass
• Manual: run gogcli inside a proxy-gated sandbox and verify Gmail API calls succeed

🤖 Generated with Claude Code

[seasonhuang]

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