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/atomics/expected/1700-atomics-load-store.exit

@@ -0,0 +1 @@
+0

examples/atomics/expected/1700-atomics-load-store.stderr

@@ -0,0 +1 @@
+

examples/atomics/expected/1700-atomics-load-store.stdout

@@ -0,0 +1,3 @@
+init: 7
+after store: 42
+incremented: 43

examples/atomics/expected/1701-atomics-rmw.exit

@@ -0,0 +1 @@
+0

examples/atomics/expected/1701-atomics-rmw.stderr

@@ -0,0 +1 @@
+

examples/atomics/expected/1701-atomics-rmw.stdout

@@ -0,0 +1,13 @@
+old add: 10
+old sub: 15
+now: 12
+old and: 240
+old or:  48
+old xor: 51
+now: 60
+old min: 20
+old max: 8
+now: 15
+runtime signed max(-5,3): 3
+runtime signed min(-5,3): -5
+comptime signed max(-5,3)=3 min(-5,3)=-5

examples/atomics/expected/1702-atomics-cas.exit

@@ -0,0 +1 @@
+0

examples/atomics/expected/1702-atomics-cas.stderr

@@ -0,0 +1 @@
+

examples/atomics/expected/1702-atomics-cas.stdout

@@ -0,0 +1,3 @@
+cas ok, now: 20
+cas failed, actual: 20, still: 20
+after loop: 105

examples/atomics/expected/1703-atomics-swap.exit

@@ -0,0 +1 @@
+0

examples/atomics/expected/1703-atomics-swap.stderr

@@ -0,0 +1 @@
+

examples/atomics/expected/1703-atomics-swap.stdout

@@ -0,0 +1,3 @@
+swap old: 7
+swap now: 42
+comptime swap: 742

examples/atomics/expected/1704-atomics-fence.exit

@@ -0,0 +1 @@
+0

examples/atomics/expected/1704-atomics-fence.stderr

@@ -0,0 +1 @@
+

examples/atomics/expected/1704-atomics-fence.stdout

@@ -0,0 +1 @@
+after fences: 3

examples/atomics/expected/1705-atomics-bool-byte-promoted.exit

@@ -0,0 +1 @@
+0

examples/atomics/expected/1705-atomics-bool-byte-promoted.stderr

@@ -0,0 +1 @@
+

examples/atomics/expected/1705-atomics-bool-byte-promoted.stdout

@@ -0,0 +1,3 @@
+init: false
+after store: true
+after reset: false