fix(deploy): the gate reads the plan schema this checkout declares

[chrishayuk]

The first categorical deploy witness failed — on a hardcoded number, not on the deployment.

The gate asserted plan schema 4. PLAN_SCHEMA is now 6, moved by the
architecture-conformance work. A gate that goes red because the format advanced is a gate
people learn to ignore.

The expected value now comes from PLAN_SCHEMA in this checkout's source. That is sound
because of the revision assertion added in #401: the gate has already confirmed the live
server is this commit, so the constant here is the constant it was built from.

Same mistake the cache tests made with PLANNER_SEMANTICS_VERSION one rung earlier —
hardcoding a value the code derives asserts today's number rather than the agreement between
the two.

Run from outside a checkout, the number can't be read; the gate still refuses a document
carrying no schema but says the number went unverified rather than passing as though checked.

The witness, now complete

== https://vindex3-explorer.fly.dev ==
  ok    capabilities schema 1
  ok    live server IS 3cd1207aedab7a815d2890803efb946964eb9e06
  ok    profile public_explorer
  ok    promises: sources.plan.hf = true
  ok    promises: sources.plan.local = false
  ok    public surface executes, binds and encodes nothing
  ok    plan schema 6, as this checkout declares
  ok    pinned at c1899de289a0... (Qwen3-0.6B)
  ok    judged by larql-vindex 0.2.0 · semantics 6
  ok    read 11.47 MB standing in for 1.50 GB (1.40 GiB)
  ok    verdict is cacheable (every artifact pinned)
  ok    second ask served from the verdict cache
  ok    a hit costs 0.18s of server work (0.27s minus a 0.10s network floor), under 0.5s
  ok    local-path planning refused 403, as advertised

PASS

Every link asserted rather than inferred: which code is live, what it judged, how it judged
it, and that the important path still behaves.