refactor: replace 899 lines of script generation with templates

Created InstallTemplateService with clean template-based script generation.
Added linux.sh.tmpl and windows.ps1.tmpl for install scripts.
Removed massive generateLinuxScript and generateWindowsScript functions.
Downloads handler now uses template service (1073 lines → 174 lines).
Templates easily maintainable without modifying Go code.

aggregator-server/internal/services/templates/install/scripts/linux.sh.tmpl

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+#!/bin/bash
+# RedFlag Agent Installer - Linux
+# Generated for agent: {{.AgentID}}
+# Platform: {{.Platform}}
+# Version: {{.Version}}
+
+set -e
+
+AGENT_ID="{{.AgentID}}"
+BINARY_URL="{{.BinaryURL}}"
+CONFIG_URL="{{.ConfigURL}}"
+INSTALL_DIR="/usr/local/bin"
+CONFIG_DIR="/etc/redflag"
+SERVICE_NAME="redflag-agent"
+VERSION="{{.Version}}"
+
+echo "=== RedFlag Agent v${VERSION} Installation ==="
+echo "Agent ID: ${AGENT_ID}"
+echo "Platform: {{.Platform}}"
+echo "Installing to: ${INSTALL_DIR}/${SERVICE_NAME}"
+echo
+
+# Step 1: Create directories
+echo "Creating directories..."
+sudo mkdir -p "${CONFIG_DIR}"
+sudo mkdir -p "/var/lib/redflag"
+sudo mkdir -p "/var/log/redflag"
+
+# Step 2: Download agent binary
+echo "Downloading agent binary..."
+sudo curl -sSL -o "${INSTALL_DIR}/${SERVICE_NAME}" "${BINARY_URL}"
+sudo chmod +x "${INSTALL_DIR}/${SERVICE_NAME}"
+
+# Step 3: Download configuration
+echo "Downloading configuration..."
+sudo curl -sSL -o "${CONFIG_DIR}/config.json" "${CONFIG_URL}"
+sudo chmod 600 "${CONFIG_DIR}/config.json"
+
+# Step 4: Create systemd service
+echo "Creating systemd service..."
+cat <<EOF | sudo tee /etc/systemd/system/${SERVICE_NAME}.service
+[Unit]
+Description=RedFlag Security Agent
+After=network.target
+
+[Service]
+Type=simple
+User=root
+ExecStart=${INSTALL_DIR}/${SERVICE_NAME}
+Restart=always
+RestartSec=30
+
+[Install]
+WantedBy=multi-user.target
+EOF
+
+# Step 5: Enable and start service
+echo "Enabling and starting service..."
+sudo systemctl daemon-reload
+sudo systemctl enable ${SERVICE_NAME}
+sudo systemctl start ${SERVICE_NAME}
+
+echo
+echo "✓ Installation complete!"
+echo "Agent is running. Check status with: sudo systemctl status ${SERVICE_NAME}"
+echo "View logs with: sudo journalctl -u ${SERVICE_NAME} -f"

aggregator-server/internal/services/templates/install/scripts/windows.ps1.tmpl

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+# RedFlag Agent Installer - Windows PowerShell
+# Generated for agent: {{.AgentID}}
+# Platform: {{.Platform}}
+# Version: {{.Version}}
+
+param(
+    [Parameter(Mandatory=$false)]
+    [switch]$SkipServiceInstall = $false
+)
+
+$AgentID = "{{.AgentID}}"
+$BinaryURL = "{{.BinaryURL}}"
+$ConfigURL = "{{.ConfigURL}}"
+$InstallDir = "C:\Program Files\RedFlag"
+$ConfigDir = "C:\ProgramData\RedFlag"
+$ServiceName = "RedFlagAgent"
+$Version = "{{.Version}}"
+
+Write-Host "=== RedFlag Agent v$Version Installation ===" -ForegroundColor Cyan
+Write-Host "Agent ID: $AgentID"
+Write-Host "Platform: {{.Platform}}"
+Write-Host "Installing to: $InstallDir\redflag-agent.exe"
+Write-Host
+
+# Step 1: Create directories
+Write-Host "Creating directories..." -ForegroundColor Yellow
+New-Item -ItemType Directory -Force -Path $InstallDir | Out-Null
+New-Item -ItemType Directory -Force -Path $ConfigDir | Out-Null
+New-Item -ItemType Directory -Force -Path "$ConfigDir\state" | Out-Null
+New-Item -ItemType Directory -Force -Path "$ConfigDir\logs" | Out-Null
+
+# Step 2: Download agent binary
+Write-Host "Downloading agent binary..." -ForegroundColor Yellow
+$BinaryPath = Join-Path $InstallDir "redflag-agent.exe"
+Invoke-WebRequest -Uri $BinaryURL -OutFile $BinaryPath -UseBasicParsing
+
+# Step 3: Download configuration
+Write-Host "Downloading configuration..." -ForegroundColor Yellow
+$ConfigPath = Join-Path $ConfigDir "config.json"
+Invoke-WebRequest -Uri $ConfigURL -OutFile $ConfigPath -UseBasicParsing
+
+# Step 4: Set permissions
+Write-Host "Setting file permissions..." -ForegroundColor Yellow
+icacls $ConfigPath /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" /grant:r "Administrators:(OI)(CI)F" | Out-Null
+
+# Step 5: Install Windows service (if not skipped)
+if (-not $SkipServiceInstall) {
+    Write-Host "Creating Windows service..." -ForegroundColor Yellow
+
+    # Register service with appropriate credentials
+    if ([System.Environment]::OSVersion.Version.Major -ge 10) {
+        # Windows 10/Server 2016+ - can use LocalService
+        New-Service -Name $ServiceName -BinaryPathName $BinaryPath -DisplayName "RedFlag Security Agent" -Description "RedFlag Security Monitoring Agent" -StartupType Automatic | Out-Null
+    } else {
+        # Older Windows - use LocalSystem
+        New-Service -Name $ServiceName -BinaryPathName $BinaryPath -DisplayName "RedFlag Security Agent" -Description "RedFlag Security Monitoring Agent" -StartupType Automatic | Out-Null
+    }
+
+    Write-Host "Starting service..." -ForegroundColor Yellow
+    Start-Service -Name $ServiceName
+}
+
+Write-Host
+Write-Host "✓ Installation complete!" -ForegroundColor Green
+Write-Host "Agent is running. Check status with: Get-Service $ServiceName"
+Write-Host "View logs with: Get-Content $ConfigDir\logs\agent.log -Tail 100 -Wait"