Stop scripts reporting success after doing nothing

A run_script command was judged solely on PowerShell's exit code, and
PowerShell treats most errors as non-terminating: it writes the error,
runs the next line, and still exits zero. The account-provisioning
script reported succeeded having provisioned nothing, and because no
output was captured there was no evidence to contradict the verdict.

Scripts now carry an errormode. Strict prepends $ErrorActionPreference
= 'Stop' so the first error ends the run and the exit code means what
it says. It is opt-in per script rather than global because bodies
authored against the permissive semantics rely on them - tolerating a
failing cleanup, probing with a cmdlet that errors when a thing is
absent, looping past a bad item - and would start aborting midway,
leaving endpoints half-configured. The default is unchanged, so every
existing script keeps running exactly as before.

The prologue is applied after digest verification, so the SHA-256 still
validates the bytes the server delivered.

stdout/stderr is captured on both paths: redirected streams for SYSTEM,
a transcript file under the ShopFloor profile for user-session runs,
since CreateProcessAsUser cannot inherit the service's pipes across the
session boundary. Output is always logged locally and returned to the
server only on failure, so routine output stays on the machine that
produced it instead of filling command history.

Also adds the optional per-script working directory, which the same
surfaces needed, and a collapsible explainer on the scripts page - the
dropdown is not self-explanatory, and an operator who does not know
about non-terminating errors has no reason to ever leave the default.

Agent 1.14.0. An older agent ignoring errormode keeps today's behaviour.

plugins/endpoints/api/routes.py

@@ -2070,9 +2070,15 @@ def _resolve_run_script(target):
     """Resolve a run_script target to a script delivery descriptor.
 
     Accepts either "script:<scriptid>" or a bare script name. The descriptor
-    carries a collector-authenticated download URL, the body's SHA-256, and the
-    per-script run context (system or user). The agent fetches the body with
-    its collector credential and runs it; the body never crosses the wire.
+    carries a collector-authenticated download URL, the body's SHA-256, the
+    per-script run context (system or user), and the optional folder to run in.
+    The agent fetches the body with its credential and runs it; the body never
+    crosses the wire.
+
+    workingdirectory is sent even when empty so the field is always present in
+    the claim: an agent that receives it and ignores it is then distinguishable
+    from one that never saw it, which matters while agents of both vintages are
+    in the field. errormode rides the same rule, and for the same reason.
     """
     kind, _sep, raw = str(target or '').partition(':')
     script = None
@@ -2100,6 +2106,8 @@ def _resolve_run_script(target):
         'installpath': '/api/endpoints/scriptbody/{}'.format(script.scriptid),
         'sha256': script.sha256,
         'runcontext': script.runcontext,
+        'workingdirectory': script.workingdirectory or '',
+        'errormode': script.errormode or 'default',
     }, None