0.2.26: security hardening from audit (P2/P3 fixes)

Address the security-auditor findings the user selected (items 2, 3, 4):

Default admin credentials (P2): remove the fixed `Ten31` default. First
boot now generates a strong random admin password (secrets.token_urlsafe),
records it 0600 at /data/.admin-password, and surfaces it once via a new
"Show Initial Admin Password" StartOS action (CLI `show-admin-password`).
The stored password is cleared when the admin is reset (CLI reset-password)
or self-changes it (change-password endpoint).

Login hardening (P2): add a per-IP in-memory sliding-window rate limiter
(10 failures / 5 min -> 429 + Retry-After) in ratelimit.py; run a dummy
argon2 verify when the user is unknown so timing can't enumerate usernames;
keep a single generic 401 for unknown-user and wrong-password.

Hardening (P3): server process now runs unprivileged -- Dockerfile adds
uid 10001 appuser; start.sh (still root) chowns the mounted /data then
drops via `setpriv` before exec'ing uvicorn. Spreadsheet imports are
size-capped via storage.read_capped (413 past MAX_UPLOAD_SIZE) in the
schedule, capital preview, and batch paths. batch_import no longer returns
raw exception text (generic per-file messages).

Verified in the packed amd64 container: PID1 uvicorn runs as uid 10001,
/data owned 10001 with 0600 secrets; generated admin password retrievable
via CLI and logs in (200); 11th bad login -> 429; admin reset clears the
stored password. Tests: test_auth_hardening.py (4). Full suite 21 passed;
frontend tsc + StartOS bundle clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

deploy/start.sh

@@ -14,31 +14,54 @@ fi
 
 # Create first approver on first boot if no users exist
 if [ ! -f /data/.initialized ]; then
-  echo "First boot: running migrations and creating default approver..."
+  echo "First boot: running migrations and creating the admin account..."
 
-  # Set default credentials (user can change via CLI later)
   ADMIN_NAME="${TEN31_ADMIN_NAME:-Jonathan}"
   ADMIN_USERNAME="${TEN31_ADMIN_USERNAME:-admin}"
   ADMIN_EMAIL="${TEN31_ADMIN_EMAIL:-jonathan@ten31.xyz}"
-  ADMIN_PASSWORD="${TEN31_ADMIN_PASSWORD:-Ten31}"
 
-  python3 -m ten31portal.cli create-user \
+  # No weak default: use an operator-supplied password if given, else generate a strong random
+  # one and record it (0600) so it can be retrieved once via the "Show Initial Admin Password"
+  # action. There is no fixed default credential to guess.
+  ADMIN_PW_FILE="$(dirname "$TEN31_DB_PATH")/.admin-password"
+  if [ -n "$TEN31_ADMIN_PASSWORD" ]; then
+    ADMIN_PASSWORD="$TEN31_ADMIN_PASSWORD"
+    GENERATED=""
+  else
+    ADMIN_PASSWORD="$(python3 -c "import secrets; print(secrets.token_urlsafe(18))")"
+    GENERATED="yes"
+  fi
+
+  if python3 -m ten31portal.cli create-user \
     --name "$ADMIN_NAME" \
     --username "$ADMIN_USERNAME" \
     --email "$ADMIN_EMAIL" \
     --role approver \
     --password "$ADMIN_PASSWORD" \
-    --service-admin || true
+    --service-admin; then
+    if [ -n "$GENERATED" ]; then
+      printf '%s' "$ADMIN_PASSWORD" > "$ADMIN_PW_FILE"
+      chmod 600 "$ADMIN_PW_FILE"
+      echo "Admin '$ADMIN_USERNAME' created with a generated password."
+      echo "  Retrieve it once via the 'Show Initial Admin Password' service action, then change it."
+    else
+      echo "Admin '$ADMIN_USERNAME' created with the operator-supplied password."
+    fi
+  fi
 
   touch /data/.initialized
-  echo "Default approver created: username=$ADMIN_USERNAME"
 fi
 
 # Log level is overridable at runtime for debugging; defaults to info.
 LOG_LEVEL="${TEN31_LOG_LEVEL:-info}"
 
-# Serve frontend static files from the backend
-exec uvicorn ten31portal.main:app \
-  --host 0.0.0.0 \
-  --port 8000 \
-  --log-level "$LOG_LEVEL"
+# Hand off to the server as an unprivileged user. The platform mounts /data owned by root, so
+# (while still root) we take ownership of the data volume first, then drop privileges with
+# setpriv — the long-running server process is never root, limiting what a compromise can reach.
+if [ "$(id -u)" = "0" ]; then
+  chown -R 10001:10001 /data
+  exec setpriv --reuid=10001 --regid=10001 --clear-groups \
+    uvicorn ten31portal.main:app --host 0.0.0.0 --port 8000 --log-level "$LOG_LEVEL"
+else
+  exec uvicorn ten31portal.main:app --host 0.0.0.0 --port 8000 --log-level "$LOG_LEVEL"
+fi