M14.4: tests main gained follow the no-panic lint rules

As the branch does for older tests: `panic!("…")` instead of
`unreachable!()` in test code (clippy.toml only allows unwrap, expect and
panic there), and the integration tests main added (CLI file I/O, render
gradient text and stroke geometry, SVG export suites) opt out of the
unwrap/expect/panic lints. No test logic changed.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/vectorcraft-cli/tests/fileio.rs

@@ -1,4 +1,6 @@
 //! The CLI opens every readable format (PDF, .ai, images) through the engine's `document.open`.
+// Integration tests: unwrapping and panicking on failure is fine here, unlike in shipped code (AGENTS.md › Robustness).
+#![allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
 
 use std::process::Command;