maint: provide compressed GitHub release assets

[consideRatio]

• fixes Packaging release assets #83

Mainly implemented by claude code, except my review fix commit. It was done with the following prompt, where the command /plan-review is a skill I've asked claude code to develop in order to have it self-review something as a staff software engineer, attached below for reference.

/plan-review
Currently, the GitHub release assets we upload are uncompressed. We want to compress the mac/linux ones with      
.tar.xz and name the files to indicate platform and os, while the compressed binary should always be named sysand.               
                                                                                                                                 
So in practice, I want an executable sysand binary on mac/linux extracted, and an sysand.exe on windows.                         
                                                                                                                                 
sysand-linux-arm64.tar.xz - sysand                                                                                               
sysand-linux-x86_64.tar.xz - sysand                                                                                              
sysand-macos-arm64.tar.xz - sysand                                                                                               
sysand-macos-x86_64.tar.xz - sysand                                                                                              
sysand-windows-arm64.zip - sysand.exe                                                                                            
sysand-windows-x86_64.zip - sysand.exe

~/.claude/skills/plan-review/SKILL.md

---
name: plan-review
description: Plan a task, have it scrutinized by a staff engineer reviewer, iterate once, then present the final plan. Use when the user wants a reviewed/vetted implementation plan.
disable-model-invocation: true
argument-hint: [task description]
---

## Reviewed Plan Workflow

You are executing a structured plan-review workflow for the following task:

$ARGUMENTS

### Step 1: Draft the Plan

Enter plan mode. Explore the codebase as needed, then write a detailed implementation plan to `tasks/todo.md`. The plan should include:

- Clear problem statement
- Proposed approach with rationale
- Files to create/modify
- Step-by-step implementation checklist
- Edge cases and risks considered

### Step 2: Staff Engineer Review

Once the plan is drafted, spawn a subagent to act as a **senior staff software engineer reviewer**. Use subagent_type `general-purpose` with a prompt like:

> You are a staff software engineer reviewing an implementation plan. Read `tasks/todo.md` and the relevant codebase context. Critique the plan on:
>
> 1. **Correctness**: Will this actually solve the problem? Any logical gaps?
> 2. **Simplicity**: Is this the simplest approach? Any over-engineering?
> 3. **Risk**: What could go wrong? Missing edge cases? Migration risks?
> 4. **Maintainability**: Will this be easy to understand and modify later?
> 5. **Completeness**: Are there missing steps, tests, or documentation updates?
> 6. **Alternatives**: Is there a better approach the author didn't consider?
>
> Be direct and specific. Flag concrete issues, not vague concerns. Suggest specific improvements where possible. Read the CLAUDE.md for project conventions.

### Step 3: Iterate on the Plan

Review the staff engineer's feedback. Update `tasks/todo.md` to address valid concerns. If you disagree with a point, note your reasoning.

### Step 4: Present to User

Exit plan mode and present the final plan to the user with:

- A concise summary of the approach
- Key changes made after the staff review
- Any open questions or trade-offs that need the user's input

[andrius-puksta-sensmetry]

This will require changes to our internal release artifact signing pipeline.

[consideRatio]

@andrius-puksta-sensmetry I don't yet have agency to drive forward something related to that without further guidance, its somewhere in gitlab I presume?

EDIT: got help via chat