docs: rebrand Certifai -> Prüfwerk (user-facing name)

The product is renamed Certifai -> Prüfwerk. This changes only the user-facing
brand text in the documentation (docs/**, VitePress title/name). It does NOT
touch functional identifiers that happen to contain "certifai" (the Docker
network, Keycloak realm/client, Harbor image project, the compliance-* crate
names, or the repo name) — those are infra-coupled and need a separate,
coordinated migration.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EgxGHn22YEfQz5fLHSHkLv

docs/guide/scanning.md

@@ -1,10 +1,10 @@
 # Running Scans
 
-Scans are the primary workflow in Certifai. Each scan analyzes a repository for security vulnerabilities, dependency risks, and code structure.
+Scans are the primary workflow in Prüfwerk. Each scan analyzes a repository for security vulnerabilities, dependency risks, and code structure.
 
 ## What Happens During a Scan
 
-When a scan is triggered, Certifai runs through these phases in order:
+When a scan is triggered, Prüfwerk runs through these phases in order:
 
 1. **Clone** -- pulls the latest code from the Git remote (or clones it for the first time)
 2. **SAST** -- runs static analysis using Semgrep with rules covering OWASP, GDPR, OAuth, secrets, and general security patterns