docs: rewrite user docs, fix modal scroll, webhook URL, and sccache

Rewrite all public documentation to be user-facing only:
- Remove deployment, configuration, and self-hosting sections
- Add guide pages for SBOM, issues, webhooks & PR reviews
- Add reference pages for glossary and tools/scanners
- Add 12 screenshots from live dashboard
- Explain MCP, LLM triage, false positives, human-in-the-loop

Fix edit repository modal not scrollable (max-height + overflow-y).
Show full webhook URL using window.location.origin instead of path.
Unset RUSTC_WRAPPER in agent cargo commands to avoid sccache errors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/main.css

@@ -441,6 +441,8 @@ tr:hover {
     padding: 24px;
     max-width: 440px;
     width: 90%;
+    max-height: 85vh;
+    overflow-y: auto;
 }
 
 .modal-dialog h3 {