chore(release): bump version to 2.1.6 (build 131)

Version: CURRENT_PROJECT_VERSION 130 -> 131 (project.yml, AGENTS.md, READMEs,
docs/llms.txt).

fix(flow): host-app identification now compiles in every build configuration
(Debug, TestFlight, Release). The arbiter probe and HostAppIdentity were
DEBUG-only, so TestFlight/App Store builds never knew the host bundle id and
could not auto-return after a startflow handoff. Debug-only logging and the
Home test card are unchanged.

Also includes the pending work in the tree:
- Home: single account/setup card surface (HomeAccountSurfacePolicy/Views)
- Wide screens: voice key row and centred mic placement, iPhone Duo layout
- Keyboard: clipboard skill ranking and AI skill layout updates
- Debug: account session handoff to the Simulator (+ import script)
- Docs: portfolio assets, privacy policy URL, site/README refresh

Tests/suite-manifest.json

@@ -26,6 +26,7 @@
       "platform": "ios",
       "tests": [
         "OSGKeyboardTests/AccountAPIClientTests",
+        "OSGKeyboardTests/DebugAccountSessionHandoffTests",
         "OSGKeyboardTests/AccountCenterViewModelTests",
         "OSGKeyboardTests/AccountCreditPurchaseManagerTests",
         "OSGKeyboardTests/AccountSecurityPrimitiveTests",
@@ -152,6 +153,7 @@
         "OSGKeyboardTests/FlowPiPLossReportGateTests",
         "OSGKeyboardTests/FlowSessionWarningReportGateTests",
         "OSGKeyboardTests/FlowHomePiPStatusPolicyTests",
+        "OSGKeyboardTests/HomeAccountSurfacePolicyTests",
         "OSGKeyboardTests/FlowPiPRecoveryPolicyTests",
         "OSGKeyboardTests/FlowAdaptiveDownsamplerTests",
         "OSGKeyboardTests/FlowSessionBridgeTests",