json stringify: nested interfaces, llvm-type resolution, member_access dispatch

[cs01]

json stringify: nested interfaces, llvm-type resolution, member_access dispatch

Summary

Three gaps in JSON.stringify dispatch that caused silent wrong output or compile errors:

• Nested interface fields: emitAddFieldsToJsonObj previously loaded any non-string/non-boolean field as double, which is wrong for nested interface-typed fields (stored as i8*). Now detects nested interfaces via interfaceStructGenHasInterface and recursively builds a sub-object using csyyjson_obj_add_obj.
• LLVM-type resolution: resolveInterfaceType only checked the symbol table by variable name. Variables populated from JSON.parse<T>() have their type in the LLVM type map (%T*) but not always in symbolTable.getInterfaceType. Now falls back to extracting the interface name from the LLVM type string, enabling JSON.stringify(cfg) where cfg = JSON.parse<Config>(str).
• member_access dispatch: JSON.stringify(user.address) where address: Address previously fell through to an error. Now resolves the field's TS type by walking the parent interface's struct layout.

Test plan

• json stringify nested interface fields — roundtrips Person { name, age, address: Address { street, zip } }
• json stringify of a json parse result — parses, stringifies, re-parses Config { host, port, debug }
• All existing json stringify/parse tests pass
• npm run verify:quick passes (Stage 0 + Stage 1 self-hosting + full unit tests)