feat(php-shim): give ported exceptions PHP's class hierarchy

Ported exceptions were flat structs reached with `downcast_ref`, so
Composer's `catch (\RuntimeException $e)` only matched the exact leaf
type and `get_class($e)` had nothing to report. Each exception now
embeds an instance of the class it extends and travels inside an
`AnyThrowable`; `Catch::catch`/`catch_mut` walk that chain, and
`PhpClass::php_class_name` yields the PHP FQCN.

Dropping the `std::error::Error` impls from the exception types leaves
`AnyThrowable` as the only route into an `anyhow::Error`, so the walk
cannot be bypassed. A `no_exception_downcast` linter catches the
`downcast::<X>()` calls that would now silently answer `None`.

Three sites change behavior as a result: the `TransportException`
exit-code override reaches `MaxFileSizeExceededException`, the
`catch (\LogicException)` in findSimilar() reaches its subclasses, and
rendered exception titles carry the real class name rather than a
guess. `get_class_err()` is no longer a `todo!()`, which re-enables
FilesystemRepositoryTest::testCorruptedRepositoryFile.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 5 insertions, 7 deletions

diff --git a/crates/shirabe/src/io/base_io.rs b/crates/shirabe/src/io/base_io.rs
index 5dd7682f..52ef9a82 100644
--- a/crates/shirabe/src/io/base_io.rs
+++ b/crates/shirabe/src/io/base_io.rs
@@ -145,13 +145,11 @@ pub trait BaseIO: IOInterface {
                 }
 
                 if !Preg::is_match(php_regex!(r"{^[.A-Za-z0-9_]+$}"), &token_str) {
-                    return Err(anyhow::anyhow!(UnexpectedValueException {
-                        message: format!(
-                            "Your github oauth token for {} contains invalid characters: \"{}\"",
-                            domain, token_str
-                        ),
-                        code: 0,
-                    }));
+                    return Err(UnexpectedValueException::new(format!(
+                        "Your github oauth token for {} contains invalid characters: \"{}\"",
+                        domain, token_str
+                    ))
+                    .into());
                 }
                 self.check_and_set_authentication(
                     domain,