Align website with the v0.116 package matrix

[GuanzhouSong]

Summary

• publish only package combinations attached to the selected official release instead of filling gaps with older releases
• narrow the Package Finder and Linux package documentation to the v0.116 Tier-1 matrix: Ubuntu 24.04 and RHEL-compatible 9, PostgreSQL 17/18, amd64/arm64
• disclose the reduced hosted package matrix and direct users to the provided packaging scripts for other distributions and PostgreSQL versions
• preserve retired APT and RPM URLs with valid empty metadata so existing package-manager configurations do not break unrelated operations
• make package and repository signing failures fatal and verify all generated signatures
• add pre-merge APT/DNF inventory and dependency-resolution smoke tests for PostgreSQL 17 and 18
• document migration and repository cleanup, with the source documentation correction in Document the v0.116 package matrix reduction docs#73

Validation

• full website test suite
• website lint and Next.js static build
• YAML schema validation
• v0.116 and pinned v0.114 repository inventory verification
• signed and unsigned APT/DNF smoke tests for PostgreSQL 17 and 18
• APT metadata, RPM package, and RPM metadata signature verification