Add --mailbox flag to mail read command

[jesseposner]

Summary

Add -m, --mailbox support to mail read so users can read messages (and list attachments) from non-default folders without changing global config.

When omitted, mail read still falls back to defaults.mailbox, so existing behavior remains unchanged.

Changes

• internal/cli/cli.go

  • Add Mailbox flag to MailReadCmd (-m, --mailbox)

• internal/cli/mail.go

  • Resolve effective mailbox as:
    • --mailbox when provided
    • otherwise config.defaults.mailbox
  • Apply effective mailbox to both:
    • GetMessage(...)
    • GetAttachments(...)

• internal/cli/help.go

  • Update mail read command schema to include --mailbox
  • Add missing --attachments and --html entries for mail read
  • Add mailbox example (pm-cli mail read 123 -m Archive)

• Docs

  • docs/commands.md: add --mailbox to mail read flags and examples
  • README.md: add mailbox-specific mail read example

• Tests

  • internal/cli/cli_test.go: extend TestMailReadCmdOptions to cover Mailbox

Why

Users often move mail into folders (Archive/custom folders). Before this change, mail read always targeted the configured default mailbox, making it awkward to read moved messages unless the default mailbox was changed.

Usage

pm-cli mail read 42 -m "Folders/Investors"
pm-cli mail read 1 --mailbox Archive --json
pm-cli mail read 10 -m "Folders/Signups" --attachments

Validation

• go test ./...