enhance(#1279): project check_violation_fixture scalar — #1278 locate + #1279 proof compose end-to-end (#1346)

Delivers option (a) from the #1314 maintainer review: thread a fourth flat
scalar check_violation_fixture through the projection so a prohibition authored
at spec-phase machine-proves fail-first and greens through the deterministic
path alone — zero hand-authoring at verify time.

- src/probe-core.cts: Prohibition gains check_violation_fixture?; projectProhibitions
  emits it (both kinds) ONLY for a well-formed descriptor and ONLY when non-empty
  (blank/absent -> projects absent -> producer hard-gates, never a partial green).
- src/prohibition-enforcement.cts: descriptorFromProjection reads it back into
  violationFixture via the same numeric-coercion-safe scalar() normalizer.
- Tests (RED-first, proven non-vacuous by reverting both src edits): CHK-02(#1346)
  projection emit, CHK-08(#1346) read-back, CHK-03(D) example round-trip, the
  fast-check round-trip property extended to the 4th scalar (the contract trek-e
  blocked #1301 on), and a real-subprocess COMPOSE capstone greening end-to-end
  through project -> descriptorFromProjection -> default prover+runner.
- Docs flipped from 'hard-gates until #1346' to 'composes end-to-end': verify-phase.md,
  prohibition-probe.md, spec-phase.md authoring, ADR-550 addendum, changeset.
  #1346 now tracks only the node-test causation residual.

190 affected-suite tests green; eslint + tsc clean; size baseline regenerated.

tests/workflow-size-baseline.json

@@ -72,7 +72,7 @@
   "ship.md": 24388,
   "sketch-wrap-up.md": 14223,
   "sketch.md": 19960,
-  "spec-phase.md": 30343,
+  "spec-phase.md": 30921,
   "spike-wrap-up.md": 15092,
   "spike.md": 24517,
   "stats.md": 6718,
@@ -85,6 +85,6 @@
   "undo.md": 10431,
   "update.md": 21053,
   "validate-phase.md": 10745,
-  "verify-phase.md": 37771,
+  "verify-phase.md": 37821,
   "verify-work.md": 31157
 }