feat(ci): add scheduled auto-release workflow

Introduce a cron-triggered auto-release workflow that runs on the second Sunday of each month,
creating a time-based tag in YYYY-MM format and dispatching the release workflow.

The release workflow is extended with a workflow_dispatch trigger accepting a tag input, so it can be
invoked both by tag pushes and programmatically by the auto-release. Version extraction is unified
via a dedicated step using `inputs.tag || github.ref_name` in both jobs.

Co-authored-by: Copilot <copilot@github.com>

README.md

@@ -24,17 +24,18 @@ Here is an example based on ubuntu 18.04 to compile a PDF file with `latexmk` fr
 root directory of your Latex files or change the `volume` option with the `${PWD}` variable.
 
 ```bash
-$ docker run \
+$ podman run \
     --rm \
-    --user="$(shell id -u):$(shell id -g)" \
     --net="none" \
-    --volume="${PWD}:/workspace" git.cryptic.systems/volker.raschek/latex:latest-archlinux \
-    latexmk \
-      -shell-escape \
-      -synctex=1 \
-      -interaction=nonstopmode \
-      -file-line-error \
-      -pdf index.tex
+    --workdir="${PWD}" \
+    --volume="${PWD}:${PWD}" \
+      git.cryptic.systems/volker.raschek/latex:latest-archlinux \
+        latexmk \
+          -shell-escape \
+          -synctex=1 \
+          -interaction=nonstopmode \
+          -file-line-error \
+          -pdf index.tex
 ```
 
 ### pdflatex
@@ -43,14 +44,15 @@ Here is a example based on ubuntu 18.04 to compile a PDF file with `pdflatex` fr
 your root directory of your Latex files or change the `volume` option with the `${PWD}` variable.
 
 ```bash
-$ docker run \
+$ podman run \
     --rm \
-    --user="$(shell id -u):$(shell id -g)" \
     --net="none" \
-    --volume="${PWD}:/workspace" git.cryptic.systems/volker.raschek/latex:latest-archlinux \
-    pdflatex \
-      -shell-escape \
-      -synctex=1 \
-      -interaction=nonstopmode \
-      -enable-write18 index.tex
+    --workdir="${PWD}" \
+    --volume="${PWD}:${PWD}" \
+      git.cryptic.systems/volker.raschek/latex:latest-archlinux \
+        pdflatex \
+          -shell-escape \
+          -synctex=1 \
+          -interaction=nonstopmode \
+          -enable-write18 index.tex
 ```