chore: Semantic Versioning and a changelog from now on

Tags become three-part (v0.6.0), the header shows the full version and
pre-release tags no longer move :stable. CHANGELOG.md (Keep a Changelog)
starts with an Unreleased section; older versions will be added from the
history. The quantity field opens the number keypad on phones.

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

.gitea/workflows/build-and-publish.yaml

@@ -4,6 +4,7 @@ name: MindSift CI & Docker Release
 #   push to dev      -> :dev
 #   push/merge main  -> :latest
 #   git tag v1.2.0   -> :v1.2.0 and :stable
+#   git tag v1.2.0-rc.1 (pre-release) -> :v1.2.0-rc.1 only, :stable stays
 on:
   push:
     branches:
@@ -39,6 +40,7 @@ jobs:
 
           # All tags of this run (space separated)
           case "${GITHUB_REF:-}" in
+            refs/tags/*-*) TAGS="${DOCKER_TAG}" ;;
             refs/tags/*)  TAGS="${DOCKER_TAG} stable" ;;
             refs/heads/main) TAGS="latest" ;;
             *)            TAGS="${DOCKER_TAG}" ;;