ci: drop container: for Godot jobs, install via composite action

The first Gitea Actions runs failed at actions/checkout@v4 because
barichello/godot-ci:4.6 ships without Node.js, which the JS-based
checkout action requires. Rather than chase a Godot CI image that
bundles Node, drop the container: blocks entirely: the default
catthehacker/ubuntu:act-latest runner image already has Node /
Python / git / JDK, and Godot is installed per-job from the
official GitHub release.

Pulled the install logic into a local composite action at
.gitea/actions/setup-godot/ to avoid duplicating 15 lines of wget +
unzip across the three Godot-using jobs. Inputs:
  - version  (default 4.6)
  - templates (default false — export jobs flip to true)

Other tweaks:
- export-android now puts $ANDROID_HOME under $GITHUB_WORKSPACE so
  no sudo is needed; editor_settings-4.tres interpolates that path.
- export-android writes the keystore under /tmp instead of /root
  (catthehacker runners don't run as root).

README updated: jobs table reflects the new "Tooling installed by the
job" column, prerequisites no longer mention the Docker image, and
known-issue #1 is closed out with the dated fix.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/actions/setup-godot/action.yml

@@ -0,0 +1,43 @@
+name: Setup Godot
+description: Download a Godot headless Linux binary and (optionally) export templates.
+
+inputs:
+  version:
+    description: Godot version (e.g. 4.6). Templates land under <version>.stable.
+    required: false
+    default: "4.6"
+  templates:
+    description: Install export templates too. "true" / "false".
+    required: false
+    default: "false"
+
+runs:
+  using: composite
+  steps:
+    - name: Install Godot ${{ inputs.version }}
+      shell: bash
+      run: |
+        set -euo pipefail
+        VER="${{ inputs.version }}"
+        URL="https://github.com/godotengine/godot/releases/download/${VER}-stable/Godot_v${VER}-stable_linux.x86_64.zip"
+        wget -q "$URL" -O /tmp/godot.zip
+        mkdir -p "$HOME/bin"
+        unzip -q /tmp/godot.zip -d /tmp
+        mv "/tmp/Godot_v${VER}-stable_linux.x86_64" "$HOME/bin/godot"
+        chmod +x "$HOME/bin/godot"
+        echo "$HOME/bin" >> "$GITHUB_PATH"
+        "$HOME/bin/godot" --version
+
+    - name: Install export templates
+      if: inputs.templates == 'true'
+      shell: bash
+      run: |
+        set -euo pipefail
+        VER="${{ inputs.version }}"
+        URL="https://github.com/godotengine/godot/releases/download/${VER}-stable/Godot_v${VER}-stable_export_templates.tpz"
+        wget -q "$URL" -O /tmp/templates.tpz
+        DEST="$HOME/.local/share/godot/export_templates/${VER}.stable"
+        mkdir -p "$DEST"
+        unzip -q /tmp/templates.tpz -d /tmp/templates_extracted
+        mv /tmp/templates_extracted/templates/* "$DEST/"
+        ls "$DEST" | head