P1: implement missing FFI functions + fix result-code semantics (#32)

The Zig FFI (src/interface/ffi/src/main.zig) was generic scaffolding that drifted
from the Idris2 ABI, which is the source of truth
(src/interface/abi/Typedqliser/ABI/Foreign.idr and .../Types.idr).

Two core domain functions declared in Foreign.idr were missing from the Zig:

  * typedqliser_check_query  : Bits64 -> String -> Bits32 -> PrimIO Bits32
      (handle pointer, query C-string, requested safety level) -> result code.
      Validates a query against the registered schema up to the requested level
      and records the achieved certificate level on the handle.

  * typedqliser_certificate_level : Bits64 -> PrimIO Bits32
      (handle pointer) -> highest safety level the last checked query achieved
      (0 if none), within the ten cumulative type-safety levels.

Both are now exported `callconv(.C)` functions with arities/types matching the
Idris %foreign declarations exactly (the handle is threaded as a Bits64 pointer
value, reconstructed FFI-side).

Result-code semantics corrected to match Typedqliser.ABI.Types.resultToInt:
  Ok=0, Error=1, InvalidQuery=2, SchemaError=3, NullPointer=4.
The generic scaffold encoded codes 2 and 3 as invalid_param / out_of_memory,
so cross-FFI those codes meant the WRONG thing. They are renamed to
invalid_query (2) and schema_error (3) and all usages updated.

The pre-existing extra exports (build_info, free_string, get_string,
is_initialized, last_error, process, process_array, register_callback) are kept
as a harmless superset; init/free/version are unchanged in behaviour.

Verification:
  * zig test src/interface/ffi/src/main.zig -lc  -> all 8 tests pass
    (added tests exercising check_query + certificate_level, the malformed-query
     InvalidQuery path, the SchemaError path, null-handle rejection, and a
     guard pinning the result codes to resultToInt).
  * idris2 --build src/interface/abi/typedqliser-abi.ipkg  -> exit 0.


Claude-Session: https://claude.ai/code/session_019xMKB3T4Vo5FYC7Czx3JSH

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath