[Aikido] Fix shell injection detection in double-quoted regions with escaped characters

[aikido-autofix]

This patch addresses shell injection detection vulnerabilities in the command encapsulation analysis. The fix improves detection of command substitutions within double-quoted strings and properly handles escaped quote characters that should not be treated as quote delimiters. Changes were made to lib/request-processor/vulnerabilities/shell-injection/isSafelyEncapsulated.go to enhance the parseQuoteRegions function's ability to accurately identify unsafe command patterns. These improvements reduce false negatives in shell injection vulnerability detection.

✅ 1 issue fixed by this PR

Issue	Severity	Description
CodeAudit#811697768	HIGH	isSafelyEncapsulated identifies quote regions without tracking shell escape state and treats any tainted occurrence inside a double-quoted region as safe when the tainted text lacks $, backticks, backslashes, and !. Consequently, a command such as echo "$(id)" with request-derived input id is classified as safely encapsulated even though the shell executes id as a command substitution. The same parser also treats escaped quotes as quote delimiters, allowing input such as foo;id # in echo \"foo;id #\" to be classified as quoted even though the quotes are literal, the semicolon is active, and the comment suppresses the trailing quote. In either case, detectShellInjection returns before containsShellSyntax, so the PHP shell hook does not report or block the operation.