feat: HTTP registry, app/bench harnesses, and DWARF #line maps

Ship QUALITY_PLAN sessions 31–33: fetchable package index URLs, showcase
app and micro/nexus benchmarks, and debugger-friendly C codegen.

- Registry: BUX_REGISTRY accepts http(s) URLs (curl/wget → ~/.bux/cache)
- E.2: make test-apps smoke for nexus/boko/simpledb/jwt-pitbul
- E.5: benches/micro + C/Nim/Zig twins; make bench-nexus (wrk)
- E.4: HIR locs → #line .bux; default -O0 -g; --release -O2; make test-dwarf

tools/bench.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+# Run Bux micro-benchmarks + language twins (C / Nim / optional Zig). E.5
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+BUXC="$ROOT/buxc"
+RUN_NEXUS="${BENCH_NEXUS:-0}"
+
+if [[ ! -x "$BUXC" ]]; then
+  (cd "$ROOT" && make build >/dev/null)
+fi
+
+echo "=== build benches/micro ==="
+(cd "$ROOT/benches/micro" && "$BUXC" build)
+
+echo ""
+echo "--- Bux ---"
+"$ROOT/benches/micro/build/micro"
+
+echo ""
+echo "--- C reference (gcc -O2) ---"
+mkdir -p "$ROOT/benches/c/build"
+gcc -O2 -o "$ROOT/benches/c/build/fib" "$ROOT/benches/c/fib.c"
+gcc -O2 -o "$ROOT/benches/c/build/int_loop" "$ROOT/benches/c/int_loop.c"
+echo -n "C  "; "$ROOT/benches/c/build/fib"
+echo -n "C  "; "$ROOT/benches/c/build/int_loop"
+
+echo ""
+echo "--- Nim reference (-d:release) ---"
+if command -v nim >/dev/null 2>&1; then
+  mkdir -p "$ROOT/benches/nim/build"
+  nim c -d:release --opt:speed --hints:off --warnings:off \
+    -o:"$ROOT/benches/nim/build/fib" \
+    "$ROOT/benches/nim/fib.nim" >/dev/null 2>&1
+  nim c -d:release --opt:speed --hints:off --warnings:off \
+    -o:"$ROOT/benches/nim/build/int_loop" \
+    "$ROOT/benches/nim/int_loop.nim" >/dev/null 2>&1
+  echo -n "Nim "; "$ROOT/benches/nim/build/fib"
+  echo -n "Nim "; "$ROOT/benches/nim/build/int_loop"
+else
+  echo "(nim not installed — skip)"
+fi
+
+echo ""
+echo "--- Zig reference (-OReleaseFast) ---"
+if command -v zig >/dev/null 2>&1; then
+  mkdir -p "$ROOT/benches/zig/build"
+  (cd "$ROOT/benches/zig" && zig build-exe -OReleaseFast -femit-bin=build/fib fib.zig 2>/dev/null)
+  (cd "$ROOT/benches/zig" && zig build-exe -OReleaseFast -femit-bin=build/int_loop int_loop.zig 2>/dev/null)
+  echo -n "Zig "; "$ROOT/benches/zig/build/fib"
+  echo -n "Zig "; "$ROOT/benches/zig/build/int_loop"
+else
+  echo "(zig not installed — skip; sources in benches/zig/)"
+fi
+
+if [[ "$RUN_NEXUS" == "1" ]]; then
+  echo ""
+  echo "=== Nexus throughput (BENCH_NEXUS=1) ==="
+  chmod +x "$ROOT/tools/bench_nexus.sh"
+  "$ROOT/tools/bench_nexus.sh"
+fi
+
+echo ""
+if [[ "$RUN_NEXUS" == "1" ]]; then
+  echo "PASS: bench (Bux + language twins + nexus)"
+else
+  echo "PASS: bench (Bux + language twins)"
+fi