feat(cli): infer --provider from mailbox domain

[stevenobiajulu]

Summary

Closes #41. When --provider is not passed, setup / configure now infers the provider from the --mailbox domain instead of silently defaulting to Microsoft for Gmail addresses.

Priority order:

1. Explicit --provider — always wins.
2. Inferred from --mailbox domain (exact match).
3. Falls back to existing 'microsoft' default (preserves behavior for corporate/custom domains).

Domain map (exact match only, case-insensitive):

• gmail.com, googlemail.com → gmail
• outlook.com, hotmail.com, live.com, msn.com → microsoft
  (Microsoft Support groups these four as Outlook.com-family consumer domains)
• anything else → undefined (falls through to microsoft default)

When inference fires, we log once to stderr (matching the existing [email-agent-mcp] Configuring mailbox … pattern) with the matched domain so the behavior is transparent:

[email-agent-mcp] Inferred provider "gmail" from mailbox domain "gmail.com". Pass --provider to override.

Pattern matching (e.g., hotmail.*) was intentionally rejected — false-positive risk for corporate domains is not worth the marginal coverage of regional variants.

Diff scope

• packages/email-mcp/src/cli.ts — new exported helper inferProviderFromMailbox (reuses the existing normalizeMailboxValue so whitespace-padded inputs still infer); two-line change to provider resolution in runConfigure; one new stderr log line.
• packages/email-mcp/src/cli.test.ts — new describe('cli/Provider Inference') with 8 unit tests covering the domain map, case-insensitivity, whitespace, non-matching domains, and explicit non-pattern-matching (hotmail.co.uk → undefined); one new integration scenario inside the existing cli/Gmail Configure block that runs configure --mailbox test@gmail.com with no --provider and asserts both the Gmail path was taken and the inference log was emitted.

No other files touched. No package-version bump (release is batched separately).

Peer-reviewed by Gemini CLI and Codex CLI before implementation. Codex caught two issues that shaped the final plan: (1) the helper reuses normalizeMailboxValue for input trimming, and (2) the "explicit Microsoft wins" runtime test was intentionally omitted — the Microsoft mock in cli.test.ts only activates for watcher tests (via watcherMockState.mailboxes.length > 0), not configure. The precedence logic is still covered by the unit ?? chain.

Test plan

• npm run build
• npm run test:run -w @usejunior/email-mcp — 150/150 passing (9 new tests)
• npm run lint

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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