Keep the vectors beside the atoms instead of rebuilding them per query

The dense leg used to be a pair of files next to the database: a full .npy
re-encoded from every atom, re-normalized on every query, and stale the moment
anything was ingested. It is now a vec0 table inside the same SQLite file,
written in the same transaction as the atom it describes, so a memory is
queryable the instant it is remembered.

- vector_index.py maintains the table; the writer inserts, the reader never
  rebuilds. A repair scan (ely-eye build-dense-index) catches what a crash hid,
  and it is not on the search path.
- Ranking stays in the engine; every boundary (closed, retired, not yet true,
  another holder's private memory, the mounted cartridge) is checked once against
  the atoms table afterwards. A visibility subquery inside the KNN cost 48.9s on
  153,857 vectors; the same check over 200 candidates costs 0.2ms. When the
  boundaries reject enough candidates the ask widens once, never twice.
- The Go mirror and the web panel carry the new status fields.
- bench/dense_scale.py and bench/quant_probe.py measure the leg at corpus size;
  bench/scale_check.py now works on a copy so the frozen baseline stays frozen.

Measured on the frozen 165,973-atom corpus. bench/reports/DENSE.md, QUANT.md and
SCALE.md carry the numbers and the machine they were taken on.

Gates: 285 pytest, ruff clean, pyright 0 on the touched files, go build/vet/test
and gofmt clean, frontend build and eslint clean. mypy is 25 findings against the
parent's 24: the new one is "Skipping analyzing sqlite_vec: missing library stubs",
the same class as the two existing qwen_vl_utils lines, and the repo keeps no
type: ignore anywhere.

frontend/src/components/MemoryPanel.tsx

@@ -103,7 +103,8 @@ export function MemoryPanel({ onChanged }: { onChanged: () => void }) {
       setNotice(
         `forgotten: ${report.atoms_deleted} atom${report.atoms_deleted === 1 ? '' : 's'}, ` +
           `${report.edges_deleted} links, ${report.cache_entries_cleared} cache entries` +
-          (report.vector_index_dropped ? ', dense index dropped' : ''),
+          (report.vectors_dropped ? `, ${report.vectors_dropped} dense vectors dropped` : '') +
+          (report.visual_index_dropped ? ', picture index dropped' : ''),
       );
       setResult(null);
       await loadBrowse();

frontend/src/components/SensesPanel.tsx

@@ -13,7 +13,7 @@ export function SensesPanel({ senses }: { senses: SenseStatus | null }) {
             <SenseRow
               label="dense vectors"
               state={senses.dense}
-              detail={`${formatNumber(senses.dense_covered)} of ${formatNumber(senses.store_atoms)} atoms indexed`}
+              detail={`${formatNumber(senses.dense_covered)} of ${formatNumber(senses.dense_expected)} memories with words indexed`}
             />
             <SenseRow
               label="picture embeddings"

frontend/src/types.ts

@@ -35,7 +35,7 @@ export interface MemoryStatus {
 export interface SenseStatus {
   dense: 'off' | 'missing' | 'behind' | 'current';
   dense_covered: number;
-  store_atoms: number;
+  dense_expected: number;
   picture_atoms: number;
   picture_bytes_missing: number;
   visual: 'absent' | 'stale' | 'ready';
@@ -309,7 +309,8 @@ export interface ForgetReport {
   atoms_deleted: number;
   edges_deleted: number;
   cache_entries_cleared: number;
-  vector_index_dropped: boolean;
+  vectors_dropped: number;
+  visual_index_dropped: boolean;
   affected_cartridges: Array<Record<string, unknown>>;
   reason: string;
 }