fix(research-mcp): add ResearchResource enum to Zig FFI (standards#153) (#121)

Class C ABI gap. `ResearchResource` (4 variants, `resResourceToInt` 1–4)
was Idris2-only.

`iseriser abi-verify` → exit 0 (3 enums, 6 transitions); `zig build
test` → 21/21 green.

Closes hyperpolymath/standards#153
Refs hyperpolymath/standards#92, #89

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

cartridges/research-mcp/ffi/research_ffi.zig

@@ -27,6 +27,16 @@ pub const ResearchProvider = enum(c_int) {
     custom = 99,
 };
 
+/// Research resource types — mirrors `ResearchMcp.SafeResearch.ResearchResource`
+/// + `resResourceToInt` encoding. Declared here so `iseriser abi-verify` can
+/// structurally check the encoding against the Idris2 source.
+pub const ResearchResource = enum(c_int) {
+    res_paper = 1,
+    res_author = 2,
+    res_citation = 3,
+    res_venue = 4,
+};
+
 // ═══════════════════════════════════════════════════════════════════════
 // Session State Machine
 // ═══════════════════════════════════════════════════════════════════════