fix: add event filtering to prevent rule evaluation on irrelevant GitHub events

[dkargatzis]

Overview

Implement intelligent event filtering to prevent rule engine evaluation on irrelevant GitHub events. Currently, events like branch deletions trigger rule evaluation and post comments to closed/merged PRs, causing unnecessary processing and user confusion.

Problem Statement

• Branch deletion events trigger rule evaluation for associated PRs
• Closed or merged PRs receive rule violation comments
• Events that don't require governance checks are processed unnecessarily
• Wasted API calls and processing resources on irrelevant events

Requirements

Event Filtering Logic

• Filter out events for closed/merged PRs unless explicitly required
• Skip rule evaluation for branch deletion events
• Ignore events for archived repositories
• Filter events based on PR state (closed, merged, draft)
• Skip processing for events that don't match rule event_types

Event Action Filtering

• Process only relevant PR actions (opened, synchronize, reopened)
• Skip rule evaluation for closed, locked, or converted_to_draft actions
• Filter push events to only process when relevant to active PRs
• Handle deployment events only for active environments

Implementation Points

• Add event filtering in webhook handlers before event processor dispatch
• Implement filtering logic in src/webhooks/handlers/ for each event type
• Add PR state validation in src/event_processors/pull_request.py
• Create event filter utility in src/core/utils/ for reusable filtering logic
• Update event processors to check event relevance before rule evaluation

Filter Criteria

• PR state: only process open PRs (skip closed, merged, draft unless specified)
• Branch state: skip deleted branches and non-existent refs
• Event action: only process actions that require rule evaluation
• Repository state: skip archived or disabled repositories
• Event age: optionally skip stale events beyond threshold

Implementation Notes

• Add should_process_event() utility function for centralized filtering
• Update webhook handlers to apply filters before dispatching to processors
• Add configuration for filter behavior (strict vs permissive)
• Log filtered events for debugging and monitoring
• Maintain backward compatibility for existing event processing

Acceptance Criteria

• Branch deletion events no longer trigger rule evaluation
• Closed/merged PRs don't receive rule violation comments
• Only relevant events trigger rule engine evaluation
• Filtering logic is configurable and well-documented
• Filtered events are logged for observability
• No breaking changes to existing event processing for valid events
• Performance improvement from reduced unnecessary processing