hardening: prepared statements, PHP 7.4 idioms, and security fixes

[somethingwithproof]

Hardens and modernizes ReportIt for PHP 7.4+.\n\n- Replace legacy isset() ternaries and assignment patterns with null coalescing operators.\n- Normalize report and archive request identifiers to integers.\n- Use those validated identifiers consistently in report table selection, filtering, and graph links.\n- Avoid variable shadowing in graph rendering.\n\nValidation:\n- PHP syntax check passes for view.php.

[Copilot]

Pull request overview

This PR aims to modernize several PHP idioms (moving from isset()-ternaries to ?? and ??=) and improve safety around request-derived values in the ReportIt plugin UI paths.

Changes:

• Replace isset(...) ? ... : ... patterns with null coalescing (??) across form and HTML helpers.
• Replace “initialize-if-unset” patterns with the PHP 7.4 null coalescing assignment operator (??=) for session keys and defaults.
• Introduce local request-var caching/casting in view.php for id/archive usage.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
view.php	Introduces local $id/$archive variables for request handling, and uses them in parts of report rendering.
templates.php	Refactors multiple isset ternaries to ?? and introduces ??= for template wizard/session defaults.
reportit.php	Uses ??= for default tab/session template assignment and ?? for optional owner/report ID handling.
lib/funct_validate.php	Uses ??= to initialize $_SESSION['sess_reportit'].
lib/funct_online.php	Uses ??= to preserve first custom error message in session.
lib/funct_html.php	Uses ?? for optional properties/values when composing HTML.

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