test: migrate examples to XXXX-category-name layout + split expected streams

Rename all example tests/companions to the XXXX-category-test-name scheme
(per-category 100-blocks: basic 0010, types 0100, ... errors 1000,
diagnostics 1100, ffi 1200, ffi-objc 1300, ffi-jni 1400, vectors 1500,
platform 1600). Companions and dir/C fixtures move in lockstep with their
parent test; #import/#source/#include paths rewritten to match.

Expected output now lives in examples/expected/ (a sibling dir of the
tests) split into three streams per the new convention:
  <name>.exit / <name>.stdout / <name>.stderr  (+ optional <name>.ir)

run_examples.sh rewritten: scans examples/ and issues/ for an
expected/<name>.exit marker, captures stdout and stderr separately (no
more 2>&1), compares each stream + exit + optional IR snapshot.

Behavior validated unchanged: every renamed test reproduces its prior
merged output + exit (diffs limited to file paths/basenames embedded in
diagnostics + traces, which correctly reflect the new names). Suite:
292 passed, 0 failed. 50-smoke.sx split + issue relocation + docs follow
in subsequent commits.

examples/expected/0201-generics-generic-struct.stdout

@@ -0,0 +1,14 @@
+v1: Vec3{data: [1.000000, 3.000000, 2.000000]}
+v2: [1.000000, 3.000000, 2.000000]
+buff: [0.000000, 2.000000, 3.500000, 4.000000, 0.000000]
+comp: Foo{value: 42, count: 1}
+add: [4.000000, 5.000000, 3.000000]
+v2.x: 1.000000
+v2[1]: 3.000000
+scaled: [2.000000, 6.000000, 4.000000]
+neg: [-1.000000, -3.000000, -2.000000]
+sqrt(9): 3.000000
+.user(0.500000)
+4
+16
+8