docs: add release notes for v0.1.0–v0.4.0, v0.6.0 and v0.7.0

Backfill notes for versions that had a tag but no release page, so
every version up to v0.7.1 has a GitHub/Gitea release. Tag v0.7.0 at
45b27d5 (was missing).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/release-notes/v0.4.0.md

@@ -0,0 +1,26 @@
+# v0.4.0 — Faster and more stable
+
+## ✨ Improvements
+
+**Section slider stays responsive on big files**
+* Dragging the section slider on large assemblies no longer freezes the screen — the cut is computed in the background and shown as soon as it's ready.
+
+**Faster placement after moving parts**
+* After dragging or using the gizmo, the part settles into its new position much faster. The interference check's gap calculation is faster too.
+
+## 🐛 Bug fixes
+
+**Errors no longer close the app**
+* If something goes wrong, you now get a message and the app keeps running instead of shutting down. Details are logged to `%LOCALAPPDATA%\STPViewer\error.log`.
+* Import, rotate and interference buttons are disabled while a long task is running, so they can't be triggered twice by accident.
+
+## 📦 Downloads
+
+Source only — no prebuilt binaries were published for this version. For a ready-to-run build, grab the [latest release](https://github.com/ETWen/STPViewer/releases/latest).
+
+## 🔗 Links
+
+* [Architecture](https://github.com/ETWen/STPViewer/blob/main/ARCHITECTURE.md)
+* [README](https://github.com/ETWen/STPViewer/blob/main/README.md)
+
+**Full changelog:** [v0.3.2...v0.4.0](https://github.com/ETWen/STPViewer/compare/v0.3.2...v0.4.0)