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.

shopdb/config.py

@@ -163,11 +163,14 @@ class Config:
     # three different routes, which makes it a property of the app rather than
     # of any handler.
     #
-    # 128 MB clears the largest thing anyone legitimately sends - the agent
-    # binary upload caps itself at 64 MB - with room for the multipart envelope.
+    # 256 MB clears the largest thing anyone legitimately sends - the agent
+    # binary upload caps itself at 128 MB - with room for the multipart
+    # envelope. This must stay STRICTLY ABOVE the agent cap: it bounds the
+    # whole request (file + boundaries + form fields), so setting the two
+    # equal would reject a file sitting exactly at the agent limit.
     # Over this, Werkzeug answers 413 without reading the body.
     MAX_CONTENT_LENGTH = int(
-        os.environ.get('MAX_CONTENT_LENGTH', 128 * 1024 * 1024))
+        os.environ.get('MAX_CONTENT_LENGTH', 256 * 1024 * 1024))
 
 
 class DevelopmentConfig(Config):