chore(testsuite): re-pin to latest (193e551) + monthly re-pin workflow (kiln#360)

[avrabe]

Resolves the kiln#360 confound and establishes the "regularly re-pin" practice.

The confound (kiln#360)

external/testsuite was unpinned: gitlink recorded c337f0d while the working tree had 7e0b83a checked out. So a fresh git worktree/CI checkout tested a different suite than the main worktree — which looked like ±18-assertion runner non-determinism but was a submodule-version mismatch. Same-commit runs are deterministic (verified: the cast cluster and full-suite non-type-subtyping results are identical across runs).

What this does

• Pins the gitlink to WebAssembly/testsuite @193e551 (latest, 2026-06-17), matching the checkout → conformance is now reproducible across CI/worktrees.
• Adds .github/workflows/testsuite-repin.yml — monthly (+ workflow_dispatch) job that bumps to latest upstream, re-runs WAST conformance, and opens a PR for review of the new baseline (spec evolution can add failing files, so it's reviewed, not auto-merged). This is the "regularly re-pin" cadence while keeping it pinned at all times.
• Updates the conformance note in architecture-components.yaml with the real, reproducible baseline.

New baseline (measured from source @193e551)

263/281 files pass; 65980 assertions pass / 529 fail. Bumping 7e0b83a → 193e551 added +184 passing assertions and +1 passing file with zero new failures — the spec evolution is strictly more coverage that kiln handles. Remaining 17 failing files dominated by the GC custom-descriptors proposal + br_on_cast/return_call_ref (Issue 149).

Note

PRs opened by the scheduled job use the default GITHUB_TOKEN, which doesn't re-trigger CI on the auto-PR — a human reviewer re-runs CI when reviewing the new baseline (acceptable, since the baseline needs human review anyway).

rivet validate: 0 errors. Refs kiln#360, #149.

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Summary

Metric	Base Branch	This PR	Change
Errors	0	0	0
Warnings	5	5	0

🎯 Impact Analysis

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