Issue: Add generic Gmail semantic search workflow

Feature Description

Add a read-only gmail.semantic_search action to the Google Workspace tool. The action should provide a reusable workflow for broad personal email requests, with domain selection, ledger-first reads, bounded Gmail scans, and normalized semantic ledger output.

Motivation

Personal currently needs special handling for broad inbox requests such as trip extraction. That does not scale to real estate closing, financial documents, tax documents, subscriptions, purchases, or other personal domains. We need a shared retrieval and ledger foundation before adding more domain-specific extractors.

Proposed Solution

• Add a domain registry to tools/google_workspace_tool.py.
• Add gmail.semantic_search as a read-only Gmail action.
• Support domain, query, refresh, full_scan, max_scan_pages, max_scan_messages, max_details, and max_age_hours.
• Return fresh ledgers before calling Gmail.
• Scan Gmail with existing gmail.scan and fetch details with gmail.get.
• Persist sanitized ledgers under HERMES_HOME/memories/.
• Add tests for ledger-first behavior, bounded scan behavior, and domain scoring.

Acceptance Criteria

• gmail.semantic_search appears in the tool schema.
• Fresh semantic ledgers bypass Gmail calls.
• Refresh or missing ledger triggers a bounded Gmail scan/search.
• The output includes records, scan stats, privacy metadata, and ledger path.
• Tests pass without live Gmail credentials.