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/0206-generics-generic-into-block.sx

@@ -0,0 +1,37 @@
+// FFI plan step 5.2 — generic `Into(Block) for Closure(..$args) ->
+// $R` impl. One impl in stdlib covers every closure shape; the
+// compiler monomorphises the impl body per call shape and emits a
+// dedicated `__invoke` `callconv(.c)` trampoline + Block literal
+// (via `#insert build_block_convert($args, $R);`).
+//
+// This test exercises a closure shape (`Closure(s64, s64) -> void`)
+// that has NO hand-rolled `Into(Block)` impl in
+// `library/modules/std/objc_block.sx`. Before step 5.2 lands,
+// `xx cl : Block` errors out with the "no Into(Block) for
+// cl_s64_s64__void" focused diagnostic. After the generic impl
+// lands, the same call resolves through the pack-shaped impl and
+// the per-shape trampoline ferries control back to the sx closure.
+//
+// The block is invoked directly through `b.invoke` (a typed
+// `callconv(.c)` fn-pointer) — the same shape the Apple Block
+// runtime calls when a UIKit/Foundation API hands the block back
+// to its registered invoke.
+
+#import "modules/std.sx";
+#import "modules/std/objc_block.sx";
+
+g_a: s64 = 0;
+g_b: s64 = 0;
+
+main :: () -> s32 {
+    cl := (a: s64, b: s64) => { g_a = a; g_b = b; };
+    blk : Block = xx cl;
+
+    invoke_fn : (*Block, s64, s64) -> void callconv(.c) = xx blk.invoke;
+    invoke_fn(@blk, 10, 20);
+
+    if g_a != 10 { print("FAIL: g_a={}\n", g_a); return 1; }
+    if g_b != 20 { print("FAIL: g_b={}\n", g_b); return 1; }
+    print("generic-into-block ok: a={} b={}\n", g_a, g_b);
+    0;
+}