Phase 5: HAMT Persistent Map + Persistent Set, 86 tests pass

- T5.3: HAMT Persistent Map (lib/cljnim_pmap.nim)
  O(log32 n) assoc/dissoc/get with structural sharing
  16 unit tests, ckMap migrated from seq to HAMT

- T5.4: Persistent Set backed by HAMT map
  ckSet with conj/disj/contains?/get, set literal #{}

- Fix: cljContains/cljCount return CljVal (not bool/int)
- Fix: equality in generics via explicit cljEq parameter
- Updated roadmap, task board, CI/Makefile

Makefile

@@ -8,6 +8,8 @@ build:
 test:
 	nim c -r tests/test_reader.nim
 	nim c -r tests/test_emitter.nim
+	nim c -r tests/test_pvec.nim
+	nim c -r tests/test_pmap.nim
 
 test-reader:
 	nim c -r tests/test_reader.nim