fix: resolve Gmail display name, QP decoding, and proxy issues

[salmonumbrella]

Summary

• Fix Google API calls bypass HTTP proxy (custom Transport missing ProxyFromEnvironment) #242: Add Proxy: http.ProxyFromEnvironment to the custom http.Transport so Google API calls respect HTTP_PROXY/HTTPS_PROXY env vars
• Fix Primary account display name not included in From header when sending (v0.9.0) #243: Fall back to People API profile name when Gmail send-as settings return an empty display name for the primary address
• Fix Email body decoding corrupts URLs containing quoted-printable-like sequences (=XX) #245: Add two-phase heuristic for quoted-printable decoding to avoid corrupting URLs containing hex-like sequences (e.g. &p=91)

Fixes #242
Fixes #243
Fixes #245

Test plan

• New test: soft line break + literal hex URL preserved by Phase 2 safety net
• New test: People API fallback for display name when send-as is empty
• New test: proxy configuration uses ProxyFromEnvironment
• New test: literal hex-like query string preserved end-to-end via Execute()
• New test: non-UTF-8 charset still decodes QP correctly
• Existing QP test (euro sign =E2=82=AC) still passes — no regression
• Full go test ./... passes

🤖 Generated with Claude Code

[steipete]

Closing as superseded by already-landed fixes on . The three intents here are already covered separately: proxy support in Google API transports (#228), Gmail primary display-name fallback (#184/#260), and the quoted-printable URL corruption fix (#186). No need to carry this stale combined branch forward.