feat: Add service-level IMAP email monitoring

[annelson-rh]

Implements IMAP email monitoring for GoAlert services with OAuth 2.0 authentication, filter rules, and alert creation.

Which issue(s) this PR fixes:
fixes: #4471

Features:

• Per-service IMAP configuration (host, port, mailbox, polling interval)
• OAuth 2.0 authentication flow in UI for Gmail
• Filter rules with pattern matching (exact, contains, regex)
• Pattern matching on From, Subject, and To fields
• Reply filtering option
• Configurable alert content (headers, from, to, subject, body)
• Email body parsing to extract clean text without MIME headers
• 1-minute minimum polling interval with per-service tracking
• Full UI for configuration and filter rule management

Database:

• Single migration: 20260213130000-imap-integration.sql
• Tables: service_imap_config, imap_filter_rules, imap_processed_messages
• Engine processing type: 'imap'

GraphQL API:

• Service.imapConfig and Service.imapFilterRules fields
• Mutations for CRUD operations on config and filter rules
• OAuth URL generation and token exchange mutations

UI Components:

• ServiceIMAPPage - main configuration page
• ServiceIMAPConfigDialog - IMAP settings with OAuth flow
• IMAPOAuthDialog - popup-based OAuth authentication
• IMAPFilterRule dialogs - create/edit/delete filter rules
• IMAPFilterRuleForm - reusable form component

Testing:

• Smoke test: test/smoke/imapmonitoring_test.go

• Cypress integration test: web/src/cypress/e2e/imapMonitoring.cy.ts

• Identified the issue which this PR solves.

• Read the CONTRIBUTING document. (apologies for not opening feature request sooner! )

• Code builds clean without any errors or warnings.

• Added appropriate tests for any new functionality.

• All new and existing tests passed.

• Added comments in the code, where necessary.

• Ran make check to catch common errors. Fixed any that came up.

⚠️ This code was generated using Claude (AI-assisted development).