feat(gmail): add --full flag to messages search to disable body truncation

[GodsBoy]

Problem

gog gmail messages search "query" --include-body truncates message bodies to 200 characters in plain-text output. For longer emails this cuts off important content, forcing users to pipe through --json and manually extract the body field.

The gmail thread get command (gog gmail read) already has a --full flag that disables its 500-character truncation, but the messages search command has no equivalent.

Solution

Add a --full flag to GmailMessagesSearchCmd that:

• Skips the 200-character truncation in sanitizeMessageBody
• Implies --include-body (so --full alone is sufficient)
• Preserves existing behaviour when --full is not passed

Usage

# Before: body truncated at 200 chars
gog gmail messages search "invoice" --include-body

# After: full body in plain-text output
gog gmail messages search "invoice" --full

Testing

• Added TestSanitizeMessageBody_FullSkipsTruncation test verifying full bodies are preserved
• Updated existing tests for the new function signature
• All tests pass (make test)
• Build passes (make build)
• Lint has one pre-existing nilnil issue in gmail_filters_helpers.go (present on main, not introduced by this PR)

Changes

• internal/cmd/gmail_messages.go: Add Full field, thread it through to sanitizeMessageBody
• internal/cmd/gmail_messages_test.go: Add full-body test, update existing test signatures