wiki: add dev-tools section with tmux, screen, and rsync articles

Add three new articles to 03-opensource/dev-tools/:
- tmux: persistent terminal sessions, background jobs, capture-pane
- screen: lightweight alternative, comparison table
- rsync: flags reference, resumable transfers, SSH usage

Update all indexes (SUMMARY, section index, main index, README).
Article count: 28 → 31. Remove tmux from writing backlog.

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

SUMMARY.md

@@ -5,6 +5,9 @@
     * [Introduction](02-selfhosting/index.md)
 * [Open Source & Alternatives](03-opensource/index.md)
     * [rmlint: Duplicate File Scanning](03-opensource/productivity/rmlint-duplicate-scanning.md)
+    * [tmux: Persistent Terminal Sessions](03-opensource/dev-tools/tmux.md)
+    * [screen: Simple Persistent Sessions](03-opensource/dev-tools/screen.md)
+    * [rsync: Fast, Resumable File Transfers](03-opensource/dev-tools/rsync.md)
 * [Streaming](04-streaming/index.md)
     * [Introduction](04-streaming/index.md)
 * [Troubleshooting](05-troubleshooting/index.md)