Add manual-only trigger event type

[dcramer]

Background

Currently, triggers are configured with events like pull_request, issues, issue_comment, and schedule. These all run automatically based on GitHub events or cron schedules. There's no way to define a skill that only runs when explicitly invoked via the warden CLI.

Requirements

Add a new manual event type that:

1. Never runs automatically - Not triggered by GitHub events or schedules
2. Only runs via CLI - Activated when running warden command locally
3. Supports same filters - Path patterns, ignorePaths, etc. should still work

Decisions

• Event name: manual ✓
• Invocation: Hybrid approach ✓
  • warden runs all event = "manual" triggers
  • warden --trigger <name> runs specific trigger
  • ⚠️ TODO: Evaluate this UX more thoroughly before finalizing

Open Questions

• Should manual triggers be able to specify a target (single file, directory, etc.)?
• Does actions field make sense for manual? Probably not required.

Config Example

[[triggers]]
name = "security-audit"
event = "manual"
skill = "security-review"

[triggers.filters]
paths = ["src/**/*.ts"]

Implementation Notes

• Update TriggerSchema in src/config/schema.ts to accept manual event
• Update matchTrigger in src/triggers/matcher.ts to handle manual events
• Update CLI to invoke manual triggers (may need new subcommand or flag)
• Consider how this interacts with existing --skill flag for running arbitrary skills