fix(desktop): Gmail import deadlock on large mailboxes (#8797)

[kodjima33]

Bug

The macOS Gmail/Email connector hangs indefinitely on Importing… / Connecting to Gmail and never completes — no counts, no error (#8797, p0).

Root cause

GmailReaderService.fetchGmailViaAtomFeedSingle launched the Python helper, then:

try process.run()
process.waitUntilExit()
let output = pipe.fileHandleForReading.readDataToEndOfFile()

When the helper prints a large JSON payload (up to 300 emails) to stdout, the pipe buffer fills, the child blocks in write(2), and the parent blocks in waitUntilExit() — a classic pipe deadlock. The UI spins forever with no timeout/error path.

Fix

• Drain stdout/stderr asynchronously via readabilityHandler while the helper runs, then waitUntilExit() — the child can never block on a full buffer.
• Add a 60s terminate timeout so a stuck/slow helper surfaces an actionable error ("produced no output") instead of hanging.
• Mirrors the vetted safe pattern already used in CalendarReaderService.

Scope: one file (+ changelog fragment), ~40 lines. Compiles clean (xcrun swift build -c debug, Build complete).

🤖 automated by hourly watchdog; opened for review, not merged.

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}