Extends the Gmail piece with the missing actions and triggers from #8072.

New actions:

• Add Label to Email — attach a label to an email
• Remove Label from Email — strip a label from an email
• Create Label — create a new user label
• Archive Email — remove INBOX label (move to All Mail)
• Delete Email — move email to Trash
• Remove Label from Thread — remove a label from all messages in a thread

New trigger:

• New Starred Email — fires when an email gets starred (checks within last 2 days, uses History API)

Other changes:

• Registered the existing but unregistered Get Thread action
• Registered the existing but unregistered New Conversation trigger
• Added gmail.modify scope needed for label/archive/delete operations
• Bumped piece version to 0.12.0

All new code follows the existing patterns — uses googleapis client, OAuth2Client, and the shared props/helpers.

/claim #8072