ci(live-provers): drop continue-on-error on Tier-2/3 live-test steps (#118)

## Summary

The two "Run live test for \${{ matrix.backend }} (allow-fail while
Wave-X wires up)" steps in `.github/workflows/live-provers.yml` carried
`continue-on-error: true`. The comments explicitly disclosed the
soft-fail as transitional, but the gate silently masks real prover
regressions: a successful Tier-2 / Tier-3 matrix run reports PASS even
when the `cargo test` step crashed with a real prover error.

This is the same anti-pattern class as echo-types' N5Falsifier xfail
gate (resolved via echo-types#136): a self-decaying CI assertion that
masks proof-validity once the underlying state matures.

## Scope

- Removed `continue-on-error: true` from the Tier-2 live-test step (line
280).
- Removed `continue-on-error: true` from the Tier-3 live-test step (line
403).
- Renamed both steps to drop the "(allow-fail while Wave-X wires up)"
qualifier.

## What is NOT changed

Intentional environment resilience preserved:
- Job-level `continue-on-error` on tier1-guix / tier3 / tier4 /
tier4-gpu (best-effort prover installations).
- Step-level `continue-on-error` on "Provision \${{ matrix.backend }}"
steps (apt installation of 30+ heterogeneous provers is genuinely
best-effort).
- Step-level `continue-on-error` on the Tier-4-GPU "Run live version
check (SKIP if binary absent)" step (version check is best-effort by
design).

## Verification

YAML lints clean. No Agda/Coq/Lean files touched — this is a CI-policy
change only.

## Refs

Estate prover-CI hygiene audit, recorded at:
\`standards/adoption-readiness-grades/AUDIT-FINDINGS-2026-05-28.adoc\`.

## Test plan

- [ ] CI runs on this PR (will fail-fast on real prover errors instead
of silently masking).
- [ ] After merge, observe Tier-2/Tier-3 scheduled runs to confirm
honest pass/fail signal.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/live-provers.yml

@@ -276,8 +276,7 @@ jobs:
             hol-light) true ;;
             *)         "${{ matrix.backend }}" --version 2>/dev/null || true ;;
           esac
-      - name: Run live test for ${{ matrix.backend }} (allow-fail while Wave-2 wires up)
-        continue-on-error: true
+      - name: Run live test for ${{ matrix.backend }}
         run: cargo test --test live_prover_suite --features live-provers -- --nocapture ${{ matrix.backend }}
 
   # ============================================================================
@@ -399,8 +398,7 @@ jobs:
             ortools)    ortools_solve --help 2>&1 | head -n 1 || true ;;
             hol4|acl2|scip|imandra) true ;;
           esac
-      - name: Run live test for ${{ matrix.backend }} (allow-fail while Wave-3 wires up)
-        continue-on-error: true
+      - name: Run live test for ${{ matrix.backend }}
         run: cargo test --test live_prover_suite --features live-provers -- --nocapture ${{ matrix.backend }}
 
   # ============================================================================