fix(security): defense-in-depth hardening for plugin_mikrotik

[somethingwithproof]

Summary

Automated defense-in-depth hardening addressing 54 security audit findings.

• XSS: Escape request variables in HTML value attributes with html_escape_request_var()
• SQLi: Convert string-concatenated queries to prepared statements
• Deserialization: Add allowed_classes => false to unserialize() calls
• Temp files: Replace predictable rand() with tempnam()

All changes are PHP 7.0+ compatible for Cacti 1.2.x.

Test plan

• PHP lint clean on all changed files
• Verify plugin functionality after changes

[Copilot]

Pull request overview

This PR applies defense-in-depth hardening to the plugin_mikrotik plugin, focusing on reducing common injection risks (SQLi/XSS/deserialization) in Cacti 1.2.x-compatible PHP.

Changes:

• Convert some SQL statements to prepared statements in poller scripts.
• Escape the filter request variable when rendered into HTML <input value=...> attributes.
• Attempt to restrict unserialize() behavior for request-provided serialized data.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
poller_mikrotik.php	Replaces interpolated SQL with prepared statements for process tracking queries.
poller_graphs.php	Updates commented-out SQL examples to prepared-statement style (no runtime impact).
mikrotik.php	Escapes filter when echoed into HTML value attributes to reduce XSS risk.
mikrotik_users.php	Modifies request deserialization logic (currently incorrect; see comment).

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[Copilot]

The allowed_classes option is being passed to get_request_var() instead of to unserialize(). In Cacti, the 2nd argument to get_request_var() is a default value; passing an array here will make stripslashes() receive an array (PHP warning) and unserialize() will still run without allowed_classes => false, reintroducing object injection risk. Pass the options as the second parameter to unserialize() (and keep get_request_var('selected_items') returning a string).

Suggested change

	$selected_items = unserialize(stripslashes(get_request_var('selected_items', array('allowed_classes' => false))));
	$selected_items = unserialize(stripslashes(get_request_var('selected_items')), array('allowed_classes' => false));

[somethingwithproof]

Converted to draft to serialize the stack in this repo. Blocked by #90; will un-draft after that merges to avoid cross-PR merge conflicts.