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/v0.1.0.md

@@ -0,0 +1,26 @@
+# v0.1.0 — First release: STEP viewer with measurement & assembly checks
+
+## ✨ New features
+
+**Open your CAD files**
+* Import STEP, STL and DXF — several files at once. STEP assemblies show up as a tree where you can hide/show, recolor or zoom to any part.
+
+**Measure**
+* Point, distance, edge length, face, circle (radius/diameter), angle and face-to-face distance. Values come from the exact CAD geometry wherever it's available.
+
+**Check how parts fit**
+* Two-point align (move), three-point align (rotate + move), rotate 90° about an axis, and an interference check that reports overlaps or the minimum gap between parts.
+
+**More tools**
+* Section view, mm ⇄ inch switch, export measurements to CSV, and save a high-resolution screenshot.
+
+## 📦 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:** [commit history](https://github.com/ETWen/STPViewer/commits/v0.1.0)