fix(OEmbedParser): prevent TypeError when HTTP_HOST is absent or domain is null

[Copilot]

Sporadic TypeError in OEmbedParser::getDomainConfig() when HTTP_HOST is unavailable (e.g. proxy/CLI edge cases or alternative host setups).

Root cause

parse() and processOembed() could pass a nullable domain into domain-config resolution. In PHP 8 this can break on strict type expectations and in practice led to unstable behavior for edge deployments.

Changes

• Hardened domain resolution in parse() with REDAXO-aware fallback via rex_request::server(..., rex::getServer()).
• Added safe post-processing fallback in parse() so preg_replace_callback() can never leak a null return.
• Kept getDomainConfig() defensively nullable and return default config for empty/null domain.
• Simplified domain handover in processOembed() and removed redundant null-coalesce paths.
• Decoupled optional Vidstack integration defensively (class_exists / method_exists) to avoid addon-coupling issues when Vidstack is missing or incompatible.

Quality / Best Practices

• Rexstan check for lib/OEmbedParser.php: 0 errors.
• Addon version bumped to 5.6.5 in package.yml.
• Changelog updated with the new release notes in CHANGELOG.md.

[Copilot]

Pull request overview

Fixes a sporadic PHP 8 TypeError in the Consent Manager’s CKE5 oEmbed integration by ensuring domain resolution and domain-config loading remain safe when HTTP_HOST and/or rex::getServer() are unavailable (or evaluate to null), falling back to default config instead of crashing.

Changes:

• Ensure parse() never passes null as a domain by using an explicit '' fallback for rex_request::server('HTTP_HOST', ...).
• Ensure processOembed() can’t propagate null into domain config lookup by adding a final ?? '' fallback.
• Make getDomainConfig() accept ?string and early-return the default config when the domain is null/empty.