Narrow bare except blocks so real errors aren't swallowed (roadmap A4)

Replaced all 46 bare 'except:' across the package with specific exception
types, and logged the cases that indicate a real problem:

- config load/save: FileNotFoundError is the silent first-run case; other
  OSError/ValueError/UnicodeDecodeError are logged.
- ffprobe/avprobe: JSON parse failures are now logged (previously a media
  file that ffprobe couldn't read just silently failed to import); decode
  fallbacks -> UnicodeDecodeError; duration parse -> ValueError/TypeError/
  KeyError; install check -> OSError/SubprocessError.
- executor: pre_/post_function and progress-polling hooks now use hasattr
  checks, and a real exception inside a defined hook is logged instead of
  swallowed; decode fallbacks and numeric parses narrowed.
- best-effort filesystem ops (makedirs/unlink) -> OSError.
- all backend check_is_installed probes -> OSError/SubprocessError.
- shutdown: also fixes a latent NameError ('failure' was only set in the
  except branch, so a successful logind PowerOff would crash the handler).

No bare 'except:' remain. Full suite (51 tests) green; GUI starts clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/devedeng/project.py

@@ -908,16 +908,16 @@ class devede_project:
                 if self.config.disc_type == "dvd":
                     try:
                         os.unlink(os.path.join(data.path, data.name + ".iso"))
-                    except:
+                    except OSError:
                         pass
                 if (self.config.disc_type == "vcd") or (self.config.disc_type == "svcd") or (self.config.disc_type == "cvd"):
                     try:
                         os.unlink(os.path.join(data.path, data.name + ".bin"))
-                    except:
+                    except OSError:
                         pass
                     try:
                         os.unlink(os.path.join(data.path, data.name + ".cue"))
-                    except:
+                    except OSError:
                         pass
             else:
                 return
@@ -968,7 +968,7 @@ class devede_project:
         movie_folder = os.path.join(data.path, "movies")
         try:
             os.makedirs(movie_folder)
-        except:
+        except OSError:
             pass
         counter = 0
         if self.disc_type == "divx":