Migrate to new Gitea instance (gitea.wbd-rd.nl)

- Update all submodule URLs from gitea.centraal.wbd-rd.nl to gitea.wbd-rd.nl
- Add settler as proper submodule in .gitmodules
- Add agent skills, function anchors, decisions, and improvements
- Add Docker configuration and scripts
- Add manuals and third_party docs
- Update .gitignore with secrets and build artifacts
- Remove stale .tgz build artifact

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

third_party/docs/sources/README.md

@@ -0,0 +1,21 @@
+# Source Documents
+
+Place actual scientific papers, standards, and technical manuals here. Reference them from the summary files in the parent directory.
+
+## Suggested Sources to Add
+
+- IWA Scientific and Technical Report No. 1 — ASM1 (Henze et al., 1987)
+- IWA Scientific and Technical Report No. 3 — ASM2d (Henze et al., 1999)
+- IWA Scientific and Technical Report No. 9 — ASM3 (Gujer et al., 1999)
+- Takacs et al. (1991) "A dynamic model of the clarification-thickening process" Water Res. 25(10), 1263-1271
+- Astrom & Hagglund (2006) "Advanced PID Control" ISA
+- Karassik et al. "Pump Handbook" McGraw-Hill
+- Europump/Hydraulic Institute "Pump Life Cycle Costs"
+- IEC 62443 series (OT security)
+- IEC 61298 series (process measurement)
+- EU Directive 91/271/EEC (Urban Waste Water Treatment)
+- NIST SP 800-82 Rev 3 (Guide to ICS Security)
+
+## File Naming Convention
+
+`<author-year>-<short-title>.pdf` — e.g., `takacs-1991-clarification-thickening.pdf`