feat: add 3 new error entries (concurrency-timing x1, triggers x1, yaml-syntax x1)

[htekdev]

New Error Entries — Strategy 6 Round 260 (Category Gap Fill)

Targeting the 3 thinnest categories (concurrency-timing: 104, triggers: 116, yaml-syntax: 116).

ID	Title	Category
ct-105	Environment protection approval gate holds cancel-in-progress: false concurrency slot — intermediate pushes silently dropped	concurrency-timing
tr-119	repository_dispatch client_payload property names with hyphens/special chars inaccessible via expression dot-notation	triggers
ys-121	uses: field does not evaluate ${{ }} expressions — dynamic action/workflow versions not possible	yaml-syntax

Research Sources

• ct-105: GitHub docs on concurrency + environment protection rules; GitHub Community discussion on deployment starvation patterns
• tr-119: GitHub REST API docs on repository_dispatch; GitHub Actions expression syntax docs (dot-notation only, no bracket notation)
• ys-121: GitHub Actions workflow syntax docs; security hardening guide; multiple community discussions about parameterizing action versions

Dedup Notes

• ct-105: Distinct from wait-timer-cancel-in-progress-starvation.yml (ct-012) which covers cancel-in-progress: true + auto-timer. This covers cancel-in-progress: false + HUMAN approval gate that can hold the slot for hours/days.
• tr-119: Distinct from repository-dispatch-event-type-mismatch.yml which covers event type name filtering.
• ys-121: Distinct from all existing yaml-syntax entries; no existing entry covers uses: expression evaluation limitation.