docs/ci: add production DNP3 engineering contract and PR build gate

[masarray]

Summary

Strengthens DNPTester governance without changing protocol/runtime behavior.

Changes

• adds a root repository engineering contract so repo/release/workflow rules are visible before entering the app subtree
• strengthens Dnp3MasterTester/AGENTS.md with root-cause-first workflow, typed Result/Try failure handling, bounded diagnostics, explicit state ownership, UI backpressure, resource lifecycle, and regression discipline
• adds a Windows/.NET 8 pull-request build gate for the main application without packaging/publishing

Key protections

• transport-open is never treated as proof of DNP3 response
• malformed/partial protocol data fails explicitly instead of being guessed into values
• routine protocol/runtime conditions use typed status/results rather than exception-driven control flow
• high-rate callbacks do not synchronously mutate unbounded WPF collections
• diagnostics are bounded, aggregated/rate-limited, and cannot stall protocol progress
• command lifecycle, point-cache, event/SOE timestamp, and evidence/report invariants remain authoritative

No product feature behavior is intentionally changed.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Trigger the build gate for the main branch

The repository's active integration branch is main—the reviewed commit's parent is the main tip, and the existing Pages workflow also listens to main—but both event filters select only master. Consequently, pull requests targeting main and pushes to main never schedule this job, so the advertised application build gate provides no protection; include main or target the actual default branch.

AGENTS.md reference: AGENTS.md:L20-L24

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