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

apps/simpledb/README.md

@@ -50,10 +50,9 @@ Data is stored as plain text, one `key=value` per line. The file is created auto
 ## Build
 
 ```sh
-# workaround: disable broken JWT module
-mv ../../lib/crypto/jwt.bux ../../lib/crypto/jwt.bux.bak
+cd apps/simpledb
 ../../buxc build
-mv ../../lib/crypto/jwt.bux.bak ../../lib/crypto/jwt.bux
+./build/simpledb data.db set hello world
 ```
 
 ## API