test: group examples into per-category folders

Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.

examples/basic/expected/0019-basic-dot-shorthand.stdout

@@ -0,0 +1,41 @@
+--- tagged enum compat ---
+T1: 3.140000
+T2: 3
+T3: 5.000000 3.000000
+T4: 2.710000
+T5: 9.500000
+T6: 4.199999
+T7a: 1.000000
+T7b: 2.000000 3.000000
+T7c: 3
+T8a: 10
+T8b: 20
+T8c: 30
+T9: 42
+T10a: 1
+T10b: 1.000000
+T10c: 9.000000
+--- struct static shorthand ---
+S1: 3.000000 4.000000
+S2: 5.000000 6.000000
+S3: 7.000000 8.000000
+S4: 0.000000 0.000000
+S4: 1.000000 0.000000
+S5: 60
+S6: 8.000000 8.000000 8.000000 8.000000
+S6: 8.000000 16.000000 8.000000 16.000000
+S6: 0.000000 12.000000 0.000000 12.000000
+S7: 7
+S8: 3.000000 4.000000
+S8q: 1.000000 2.000000
+S9: 4.000000 6.000000
+S10: 4.000000 6.000000
+--- edge cases ---
+E1: 5.000000 1.000000 2.000000
+E2: 9 1.000000 2.000000
+E3: 1
+E4: 4.000000 6.000000
+E5: 42
+E6: 1
+E7: 20.000000 10.000000
+=== DONE ===