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.

TODO.md

@@ -0,0 +1,73 @@
+# TODO: `ann` base branch + consolidated benchmarks
+
+## 1. Create `ann` branch with shared code
+
+### 1.1 Branch setup
+- [x] `git checkout -B ann origin/main`
+- [x] Cherry-pick `624f998` (vec0_distance_full shared distance dispatch)
+- [x] Cherry-pick stdint.h fix for test header
+- [ ] Pull NEON cosine optimization from ivf-yolo3 into shared code
+  - Currently only in ivf branch but is general-purpose (benefits all distance calcs)
+  - Lives in `distance_cosine_float()` — ~57 lines of ARM NEON vectorized cosine
+
+### 1.2 Benchmark infrastructure (`benchmarks-ann/`)
+- [x] Seed data pipeline (`seed/Makefile`, `seed/build_base_db.py`)
+- [x] Ground truth generator (`ground_truth.py`)
+- [x] Results schema (`schema.sql`)
+- [x] Benchmark runner with `INDEX_REGISTRY` extension point (`bench.py`)
+  - Baseline configs (float, int8-rescore, bit-rescore) implemented
+  - Index branches register their types via `INDEX_REGISTRY` dict
+- [x] Makefile with baseline targets
+- [x] README
+
+### 1.3 Rebase feature branches onto `ann`
+- [x] Rebase `diskann-yolo2` onto `ann` (1 commit: DiskANN implementation)
+- [x] Rebase `ivf-yolo3` onto `ann` (1 commit: IVF implementation)
+- [x] Rebase `annoy-yolo2` onto `ann` (2 commits: Annoy implementation + schema fix)
+- [x] Verify each branch has only its index-specific commits remaining
+- [ ] Force-push all 4 branches to origin
+
+---
+
+## 2. Per-branch: register index type in benchmarks
+
+Each index branch should add to `benchmarks-ann/` when rebased onto `ann`:
+
+### 2.1 Register in `bench.py`
+
+Add an `INDEX_REGISTRY` entry. Each entry provides:
+- `defaults` — default param values
+- `create_table_sql(params)` — CREATE VIRTUAL TABLE with INDEXED BY clause
+- `insert_sql(params)` — custom insert SQL, or None for default
+- `post_insert_hook(conn, params)` — training/building step, returns time
+- `run_query(conn, params, query, k)` — custom query, or None for default MATCH
+- `describe(params)` — one-line description for report output
+
+### 2.2 Add configs to `Makefile`
+
+Append index-specific config variables and targets. Example pattern:
+
+```makefile
+DISKANN_CONFIGS = \
+    "diskann-R48-binary:type=diskann,R=48,L=128,quantizer=binary" \
+    ...
+
+ALL_CONFIGS += $(DISKANN_CONFIGS)
+
+bench-diskann: seed
+    $(BENCH) --subset-size 10000 -k 10 -o runs/diskann $(BASELINES) $(DISKANN_CONFIGS)
+    ...
+```
+
+### 2.3 Migrate existing benchmark results/docs
+
+- Move useful results docs (RESULTS.md, etc.) into `benchmarks-ann/results/`
+- Delete redundant per-branch benchmark directories once consolidated infra is proven
+
+---
+
+## 3. Future improvements
+
+- [ ] Reporting script (`report.py`) — query results.db, produce markdown comparison tables
+- [ ] Profiling targets in Makefile (lift from ivf-yolo3's Instruments/perf wrappers)
+- [ ] Pre-computed ground truth integration (use GT DB files instead of on-the-fly brute-force)