Fix user-context collection, split agent log destinations, widen upload cap

Mapped drives stopped reporting because the user-context path failed silently
in three separate places, and none of them left a trace to read back.

- Probe: launch via -EncodedCommand instead of staging a temp .ps1 and running
  powershell.exe -File. A missing or quarantined script file fails BEFORE any
  statement runs, so the script's own try/catch never sees it and the only
  symptom is exit -196608.
- Spool: pin to the ShopFloor profile. Resolving it through WTSQueryUserToken
  is privileged, endpoint protection blocks it, and on failure the tray
  (writer) and service (reader) silently disagree about the path.
- Spool: consume after a successful parse, so a stopped tray cannot keep
  re-reporting stale mapped drives as current. Unparseable files are left in
  place for the next cycle.
- Logging: user-session components cannot write to Program Files or to the
  SYSTEM-owned ProgramData log directory, and the file sink degrades to a
  silent no-op when it cannot create its directory. Tray and probe now log to
  C:\Users\ShopFloor\ShopDB\Logs, installs transcript to ProgramData, and the
  sink records a SinkProblem instead of swallowing UnauthorizedAccessException.
- Installer: provision the operator spool/log directories with ShopFloor:Modify
  before the tray first runs, and stop the transcript via trap so a throw
  cannot orphan exactly the failed install worth reading.
- Upload cap 64 -> 128 MB: the self-contained tray publishes at ~69 MB and was
  rejected on SIZE, but the size check returns before the PE is parsed, so the
  operator only ever saw a version-detection failure.

AGENT-CONTRACT.md gains a normative section defining the three security
contexts, their log destinations, the fixed spool path and consume-on-read.

Agent 1.8.0 -> 1.8.1, tray 1.1.0 -> 1.1.1 so the deployed build is
identifiable from a log line.

tests/test_plugin_migrations.py

@@ -103,7 +103,10 @@ EXPECTED_HEAD_REVISION['warranty'] = 'warranty0002proof'
 # 0011 adds the trayversion cache column to endpointstates.
 # 0012 adds endpointevents.eventrecordid plus the unique index that dedups a
 # replayed Windows event record.
-EXPECTED_HEAD_REVISION['endpoints'] = 'endpoints0013inventorycolumns'
+# 0013 adds the inventory columns.
+# 0014 adds endpointstates.diskhealthjson, and 0015 adds the system telemetry
+# columns (boot info, reboot reasons, Defender health, NIC link state).
+EXPECTED_HEAD_REVISION['endpoints'] = 'endpoints0015systemtelemetry'
 
 # Plugins built after the cutover: their 0001 baseline really creates tables the
 # core chain never owned.