fix: enable memory controller legacy fallback for kelvin-host in release builds

[Copilot]

Fresh users running the release binary with no memory signing keys configured hit a hard error because kelvin-host was compiled with memory_rpc active but without memory_legacy_fallback, leaving no recovery path when RPC connection/validation fails.

Root Cause

The release build compiles all binaries in a single cargo build invocation:

cargo build ... -p kelvin-host -p kelvin-gateway ... --features kelvin-gateway/memory_rpc

Cargo's feature unification propagates kelvin-sdk/memory_rpc (pulled in via kelvin-gateway) to kelvin-host since both share the same kelvin-sdk dep. memory_legacy_fallback was never added, so the hard-error branch fired unconditionally on any RPC failure:

#[cfg(not(feature = "memory_legacy_fallback"))]
{
    return Err(KelvinError::Backend(format!(
        "memory controller unavailable and legacy fallback disabled: {err}"
    )));
}

Changes

• scripts/package-unix-release.sh — add kelvin-host/memory_legacy_fallback to --features
• scripts/package-windows-release.ps1 — same

--features kelvin-gateway/memory_rpc,kelvin-host/memory_legacy_fallback

With this, unconfigured or unavailable memory controllers degrade gracefully to in-process memory rather than aborting.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>BUG Memory Controller Fallback Disabled</issue_title>
<issue_description><!--
Thank you for reporting a possible bug in KelvinClaw.

Please fill in as much of the template below as you can.

Platform: output of uname -a (UNIX), or version and 32 or 64-bit (Windows)
Subsystem: if known, please specify the affected core module name

If possible, please provide code that demonstrates the problem, keeping it as
simple and free of external dependencies as you can.
-->

• Version:

From release 0.1.8 binary:

kelvinclaw-0.1.8-linux-arm64

• Platform:

Raspberry Pi: 6.12.47+rpt-rpi-v8 AgenticHighway/kelvinclaw#1 SMP PREEMPT Debian 1:6.12.47-1+rpt1 (2025-09-16) aarch64 GNU/Linux

• Subsystem:

kelvin-memory-client + kelvin-memory-controller

the memory controller fallback is disabled

Error message

[kelvin] OPENAI_API_KEY not found in the environment or .env files.
[kelvin] Paste your OpenAI API key for this run, or press Enter to continue with echo mode:
loaded kelvin core toolpack plugins: 5
loaded installed plugins: 2
error: backend failure: memory controller unavailable and legacy fallback disabled: invalid input: memory signing config requires either PEM signing material or KMS key id

Steps to reproduce

1. freshly download kelvinclaw binary from release 0.1.8
2. attempt to run ./kelvin
3. enter dummy api key and press enter</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes BUG Memory Controller Fallback Disabled #28

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