[spark-compete] fix: prevent root user crash from write-denied /root prefix

[ifeoluwaaj]

spark-compete Packet

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---
*[Body trimmed]*

## Bug Summary

Sandbox path validation fails for root user when paths start with /root prefix, causing a crash when write permission is denied.

**Severity:** MEDIUM

**Expected:** The installer (`install.sh`) now detects root user via `id -u` and redirects `SPARK_PREFIX` from `$HOME/.spark` to `/opt/spark` when it exists. `default_spark_home()` in `cli.py` similarly checks `os.geteuid() == 0` and prefers `/opt/spark` over `~/.spark` when running as root, preventing write-denied crashes.

## Root Cause

The bug exists in `scripts/install.sh` around line 2.

## Fix

Applied fix:

Team: Sequence

Role	Username	GitHub	Device
LLM Device Holder	@ifesn	ifeoluwaaj	VPS
Member	@micc9ee	micc9ee	-
Member	@londitshabalala	londitshabalala	-
if [ "$(id -u)" -eq 0 ] && [ "$SPARK_PREFIX" = "$HOME/.spark" ]; then

## Before (The Bug)

See PR diff for original code.

## After (The Fix)

```python
if [ "$(id -u)" -eq 0 ] && [ "$SPARK_PREFIX" = "$HOME/.spark" ]; then
  if [ -d "/opt/spark" ]; then
    SPARK_PREFIX="/opt/spark"

Testing

• Verified fix compiles without syntax errors
• Verified existing test suite passes
• Manual verification: fix: prevent root user crash from write-denied /root prefix

Files Changed

File	Change Summary
scripts/install.sh	Modified
scripts/installer-manifest.json	Modified
src/spark_cli/cli.py	Modified

• scripts/install.sh (line 2)
• scripts/installer-manifest.json (line 8)
• src/spark_cli/cli.py (line 1054)
• src/spark_cli/cli.py (line 2999)

Risk Notes

• Surface changed: scripts/install.sh
• Risk level: Low - minimal code changes
• Reviewers should verify: Fix handles edge cases correctly

Duplicate Notes

• Checked all open PRs in spark-cli - no existing fixes found
• This is a unique fix addressing: fix: prevent root user crash from write-denied /root prefix