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/errors/expected/1036-errors-failable-smoke.stdout

@@ -0,0 +1,23 @@
+tag: BadDigit
+parsed: 10
+got: BadDigit
+catch-expr: 100
+catch-match: 1
+or-default ok: 10
+  logged BadDigit
+or-default err: -1
+or-value: 55
+or-chain: 16
+pair-catch: 0 0
+pair-ok: 8 10
+check absorbed
+acquire fail:
+  onfail B
+  defer A
+acquire ok:
+  defer A
+closure-run: 12
+closure-run-err: -9
+widen: 10
+wrap: 42
+errors ok