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/0026-basic-operators.stdout

@@ -0,0 +1,60 @@
+=== 2. Operators ===
+add: 7
+sub: 7
+mul: 42
+div: 5
+mod: 2
+neg: -5
+eq: true
+neq: true
+lt: true
+gt: true
+le: true
+ge: true
+chain: true
+chain-gt: true
+chain-mixed: true
+eq-chain: true
+eq-chain-f: false
+band: 15
+bor: 7
+bxor: 240
+bxor2: 5
+bnot: -1
+bnot2: -2
+shl: 16
+shr: 16
+shl2: 24
+shr2: 127
+band-var: 15
+bor-var: 7
+bxor-var: 240
+shl-var: 16
+shr-var: 15
+bnot-var: -16
+and-assign: 15
+or-assign: 255
+xor-assign: 240
+shl-assign: 256
+shr-assign: 16
+mod-var: 2
+and: true
+and-false: false
+or: true
+or-false: false
+short-and: false
+short-or: true
+ca+=: 15
+ca-=: 12
+ca*=: 24
+ca/=: 4
+prec1: 14
+prec2: 20
+xx-cast: 200
+widen-u8-i64: 200
+widen-i32-f64: 42.000000
+widen-f32-f64: 1.500000
+widen-u8-i16: 100
+xx-i64-i32: 12345
+xx-f64-f32: 1.500000
+xx-f64-i32: 7