fix: extend llmspec hardening safeguards

[berketpbs]

Summary

• Add a second hardening pass across size parsing, HTTP parsing, model verification, provider telemetry, persisted settings, catalog validation, and CI/release workflows
• Add regression tests and architecture documentation

Historical migration dates

Four commits were created on each requested date: July 13, 14, 15, 17, 18, 20, 22, 23, 24, and 26, 2026.

All format, Clippy, test, and catalog checks pass.