feat(simpledb): file-backed key-value database with CLI

- Add SimpleDB: plain-text key=value store with get/set/del/has/keys/count
- Fix lib/Fmt.bux: replace *(ptr+N) pointer arithmetic with ptr[N] indexing
- Fix lib/crypto/jwt.bux: use alg.tag directly instead of int-comparison

apps/simpledb/bux.toml

@@ -0,0 +1,8 @@
+[Package]
+Name    = "simpledb"
+Version = "0.1.0"
+Type    = "bin"
+Description = "SimpleDB — file-backed JSON key-value database for Bux"
+
+[Build]
+Output = "Bin"