Define specialization CFG diagnostic ordering and script attribution

[thiremani]

Context

Specialization-aware CFG replay now has deterministic depth-first traversal, reports an identical source diagnostic once per script even when multiple type/scalar variants contain it, and reports a shared .pt defect independently for each failing script.

Those mechanics are intentional, but the user-facing presentation policy is not yet explicit.

Decide and document

• whether replay order should remain call-closure DFS order or be globally sorted by source file/location
• whether the CLI trailer should say that errors came from the script and its reachable code rather than only error compiling scriptFile ...
• how a shared library/template diagnostic should be grouped when multiple scripts fail in one compiler invocation
• preserve per-script failure semantics; do not globally suppress a diagnostic and accidentally make later scripts appear successful

Acceptance tests

• two scripts reaching the same failing template retain independent failure results
• diagnostic source tokens continue to point at the .pt file
• within one script, concrete and scalar companion variants produce one identical diagnostic
• the selected ordering and trailer wording are pinned end to end

This is diagnostic-policy polish, not a correctness blocker for PR #89.