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/startos/actions/index.ts

@@ -214,6 +214,44 @@ const listUsersAction = Action.withoutInput(
   },
 )
 
+// ============================================
+// Action: Show Initial Admin Password
+// ============================================
+const showAdminPasswordAction = Action.withoutInput(
+  'show-admin-password',
+  {
+    name: 'Show Initial Admin Password',
+    description:
+      'Reveal the randomly-generated admin password created on first boot. Sign in with it, then change your password — after which this no longer shows it.',
+    warning: null,
+    allowedStatuses: 'only-running',
+    group: null,
+    visibility: 'enabled',
+  },
+  async ({ effects }) => {
+    try {
+      const result = await runCli(effects, ['show-admin-password'], 'show-admin-password-task')
+      if (result.exitCode !== 0) {
+        return errorResult(result.stderr?.toString() || 'Failed to read the admin password')
+      }
+      return {
+        version: '1' as const,
+        title: 'Initial Admin Password',
+        message: 'Sign in as "admin" with this password, then change it from the portal.',
+        result: {
+          type: 'single' as const,
+          value: (result.stdout?.toString() || '').trim() || 'No stored password.',
+          copyable: true,
+          qr: false,
+          masked: true,
+        },
+      }
+    } catch (e: any) {
+      return errorResult(`Failed to read the admin password: ${e.message || e}`)
+    }
+  },
+)
+
 // ============================================
 // Action: Delete User
 // ============================================
@@ -379,6 +417,7 @@ const resetHoldingsAction = Action.withInput(
 export const actions = sdk.Actions.of()
   .addAction(createUserAction)
   .addAction(resetPasswordAction)
+  .addAction(showAdminPasswordAction)
   .addAction(listUsersAction)
   .addAction(deleteUserAction)
   .addAction(dedupeAction)