fix: remove duplicate ara-diac-tiny spec (last-key-wins hazard)

PR #63 added a second ara-diac-tiny key; the pre-existing spec later
in the dict silently won. Keep the existing clean-label spec (snapshot
labels, gate <= 3.07).

Author: Ronald Tse

src/gpu/modal_distill.py

@@ -141,40 +141,6 @@ def _ensure_src_path() -> None:
         "mode": "sequence",
         "note": "r6 canonical (2.5793 DER); gate <= 3.07 windowed DER-CE",
     },
-    "ara-diac-tiny": {
-        # the browser/Worker tier: ~45M params -> ~45MB int8 zip. Same
-        # teacher (r6), corpus, and frozen labels as run-002 — the ONLY
-        # variable is student capacity. From-scratch risk is real (Thai
-        # ablation: scratch byt5-small plateaued ~13% PER) but this is
-        # dense CE on 30k paragraph units, not RL; gate: does not
-        # collapse (finite output, DER bounded well below scratch) and
-        # <= 5.0 windowed DER-CE would make it shippable.
-        "teacher": "rababa_arabic_byt5/run-006-morph/best",
-        "teacher_volume": "rababa",
-        "student_config": {
-            "vocab_size": 384,
-            "d_model": 384,
-            "d_ff": 1024,
-            "d_kv": 64,
-            "num_layers": 6,
-            "num_decoder_layers": 2,
-            "feed_forward_proj": "relu",
-            "decoder_start_token_id": 0,
-            "eos_token_id": 1,
-            "pad_token_id": 0,
-        },
-        "train": "r5-units/domain.txt",
-        "train_extra": ["r5-units/replay.txt"],
-        "unit_limits": [24000, 6000],
-        "max_len": 1450,
-        "label_beams": "1",
-        "out": "rababa_arabic_distill_tiny/run-001",
-        "labels_file": "teacher_labels_v2.jsonl",
-        "labels_complete": "true",
-        "mode": "sequence",
-        "note": "tiny-tier probe: r6 teacher, run-002 corpus/labels, "
-                "~45M student; collapse check + DER gate <= 5.0",
-    },
     "ara-diac-small-pkm": {
         # TODO.qwen-next/02 — the LongCat/Qwen capacity axis: keep the
         # ByT5-small compute, add product-key lookup memory (+~25M