App.is_installed(): Add method

The installed state of a project is judged by the proofs of installation,
which differ per subpackage: make/project.conf in the dev tree or /opt
proves the -devel package or a buildable checkout, a VERSION file in the
project directory or /usr/share/doc/packages the -run package.

Add is_installed(), which answers the proof question for a given subpackage
by searching the per-subpackage locations.

Signed-off-by: Jan Lindemann <jan@janware.com>
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.84.2

src/python/jw/pkg/App.py

@@ -98,6 +98,25 @@ class App(Base):
             return None
         raise Exception('No project path found for module "{}"'.format(name))
 
+    @cache
+    def __is_installed(self, name: str, devel: bool) -> bool:
+        # devel: the project is in the dev tree or the -devel
+        # package is installed: make/project.conf is present.
+        # run: the -run package is installed: a VERSION file is
+        # present in the project directory or
+        # /usr/share/doc/packages.
+        search, file = (
+            (self.__projs_root, self.___opt_root),
+            '/make/project.conf'
+        ) if devel else (
+            (self.__projs_root, '/usr/share/doc/packages'),
+            '/VERSION'
+        )
+        for root in search:
+            if root is not None and os.path.exists(f'{root}/{name}{file}'):
+                return True
+        return False
+
     def __find_dir(
         self,
         name: str,
@@ -404,6 +423,18 @@ class App(Base):
             raise Exception('No distro object')
         return self.__distro
 
+    def is_installed(
+        self,
+        name: str,
+        devel: bool = False,
+    ) -> bool:
+        """True if the project is installed: for devel,
+        make/project.conf is present in the dev tree or /opt; for
+        run, a VERSION file is present in the project directory
+        or /usr/share/doc/packages.
+        """
+        return self.__is_installed(name, devel)
+
     def find_dir(
         self,
         name: str,