Add ANN search support for vec0 virtual table

Add approximate nearest neighbor infrastructure to vec0: shared distance
dispatch (vec0_distance_full), flat index type with parser, NEON-optimized
cosine/Hamming for float32/int8, amalgamation script, and benchmark suite
(benchmarks-ann/) with ground-truth generation and profiling tools. Remove
unused vec_npy_each/vec_static_blobs code, fix missing stdint.h include.

benchmarks-ann/Makefile

@@ -0,0 +1,61 @@
+BENCH = python bench.py
+BASE_DB = seed/base.db
+EXT = ../dist/vec0
+
+# --- Baseline (brute-force) configs ---
+BASELINES = \
+	"brute-float:type=baseline,variant=float" \
+	"brute-int8:type=baseline,variant=int8" \
+	"brute-bit:type=baseline,variant=bit"
+
+# --- Index-specific configs ---
+# Each index branch should add its own configs here. Example:
+#
+# DISKANN_CONFIGS = \
+# 	"diskann-R48-binary:type=diskann,R=48,L=128,quantizer=binary" \
+# 	"diskann-R72-int8:type=diskann,R=72,L=128,quantizer=int8"
+#
+# IVF_CONFIGS = \
+# 	"ivf-n128-p16:type=ivf,nlist=128,nprobe=16"
+#
+# ANNOY_CONFIGS = \
+# 	"annoy-t50:type=annoy,n_trees=50"
+
+ALL_CONFIGS = $(BASELINES)
+
+.PHONY: seed ground-truth bench-smoke bench-10k bench-50k bench-100k bench-all \
+        report clean
+
+# --- Data preparation ---
+seed:
+	$(MAKE) -C seed
+
+ground-truth: seed
+	python ground_truth.py --subset-size 10000
+	python ground_truth.py --subset-size 50000
+	python ground_truth.py --subset-size 100000
+
+# --- Quick smoke test ---
+bench-smoke: seed
+	$(BENCH) --subset-size 5000 -k 10 -n 20 -o runs/smoke \
+		$(BASELINES)
+
+# --- Standard sizes ---
+bench-10k: seed
+	$(BENCH) --subset-size 10000 -k 10 -o runs/10k $(ALL_CONFIGS)
+
+bench-50k: seed
+	$(BENCH) --subset-size 50000 -k 10 -o runs/50k $(ALL_CONFIGS)
+
+bench-100k: seed
+	$(BENCH) --subset-size 100000 -k 10 -o runs/100k $(ALL_CONFIGS)
+
+bench-all: bench-10k bench-50k bench-100k
+
+# --- Report ---
+report:
+	@echo "Use: sqlite3 runs/<dir>/results.db 'SELECT * FROM bench_results ORDER BY recall DESC'"
+
+# --- Cleanup ---
+clean:
+	rm -rf runs/