Add missing README information to centralized repo docs

[dobby-coder]

Summary

Addresses feedback from @rubenhensen on #8 — information from repo READMEs was missing in the centralized docs pages.

Audited all 16 non-archived repo READMEs against their corresponding docs/repos/*.md pages. Five repos had missing information:

• pdf-signature (specifically called out): Added frontend development setup, backend configuration table with all config options, build/run commands
• cryptify: Added backend configuration table with all config file options (server_url, address, data_dir, SMTP settings, allowed_origins, pkg_url), commands for running the built binary
• postguard: Added unaudited warning, expanded prerequisites (Rust 1.90+, Docker, wasm-pack), WASM build instructions, Docker Compose dev environment, PKG server setup with key generation and CLI flags, environment variables table, CLI usage examples (encrypt/decrypt), reference to Docusaurus site, funding section (NGI0/NLnet/NWO)
• postguard-fallback: Added dependency versions table (Rust 1.57, NGINX 1.21, PostgreSQL 12, Mailhog 1.0), links to IRMA documentation and irmaseal design document
• postguard-website: Added Docker stopping commands, docker-compose build command

The remaining 11 repos (ibe, ibs, irmaseal-mail-utils, pg-components, pg-curve, pg-example, postguard-js, postguard-dotnet, postguard-tb-addon, postguard-outlook-addon, postguard-examples) were verified to already contain all information from their READMEs.

Test plan

• Review each changed file against the original repo README to confirm all info is captured
• Build the VitePress site and verify pages render correctly
• Check that no banned words from CLAUDE.md style guide are used