fix(skeleton): declare the door back from a trial, and require a decision for every provider

[rodrigoteamx]

What was wrong

A governed session running make scaffolds into a trial workspace and answers «apply it with sandbox:promote». TrialOperations is what offers that operation — and this skeleton never declared it. Every newly created app got a scaffolder that named a command the app did not have.

It had been found three times in the greenhouse and patched each time where it surfaced, never here:

	where	what was done
decisions/0227	«not wired in the skeleton, but in three lab apps»	profiles added
decisions/0331	two authoring attempts invalidated	a catalogue check added — to the lab mount
evidence/0994	a local model removed every other obstacle and stopped on exactly this, naming it house_debt	—

What changed

TrialOperations is declared in config/operations.php.

Measured in an app created from this skeleton without milpa/agent — which is how every app is born:

before:  sandbox:* offered → 0
after:   sandbox:list · sandbox:discard · sandbox:promote · sandbox:undo
         sandbox:list → ok: yes · trials: (none)

The guard checks the shape, not the name

A guard that checks TrialOperations by name certifies that one instance and waves the next through. This one enumerates, by reflection, every concrete CommandProvider that milpa/app-runtime ships under Operations, and requires each to be declared or listed in EXCUSED with a written reason — so left out and forgotten stop looking the same.

Enumerating surfaced one more provider outside the list, and it is correctly outside: PresentationOverrideOperations takes a PresentationOverrideStore in its constructor and is wired by LivePlugin, like ScreenOperations. It is excused in writing rather than flagged.

test	pins
every provider declared or excused	the shape of the defect
every excuse names a provider that still exists	an excuse outliving its provider is the same silence one step later
the door back from a trial is offered	sandbox:promote and sandbox:list, directly

How it was verified

181 tests (178 → +3) · 412 assertions · 66 skipped — the same 66 as main
phpstan clean · style clean

By mutation: dropping the TrialOperations line fails twice (the enumeration names it, and sandbox:promote goes missing); dropping the excuse fails naming PresentationOverrideOperations. The enumeration also asserts it sees AgentOperations, so an empty result cannot pass everything silently.

Greenhouse: decisions/0461.