perf(inventory): lazy list, photo thumbnails, indexes, debounced reload

Scale the local inventory to 10k+ varieties:
- Render the list with ListView.builder over a flattened header/item model
  instead of building every tile upfront.
- Store a small regenerable JPEG thumbnail per photo (schema v14) and use it
  for the 48px list avatar; full bytes stay for offer image hosting. Existing
  photos are backfilled lazily at startup. Thumbnail is local-only (excluded
  from CRDT sync and backups by the JSON codec).
- Add indexes on varieties(is_deleted,is_draft), attachments(parent_type,
  parent_id,kind), lots(variety_id) via @TableIndex.
- Debounce watchInventoryView (~250ms) so a burst of table writes triggers one
  reload, not seven.
- cacheWidth/cacheHeight on the list avatar decode.
- Scale test raised 3k -> 10k; migration test v13 -> v14.

apps/app_seeds/lib/db/tables.dart

@@ -5,6 +5,10 @@ import 'sync_columns.dart';
 
 /// The identity/accession — one row per distinct thing in the inventory.
 /// Only [label] is mandatory (progressive disclosure).
+///
+/// The index covers the inventory list's hot filter — non-deleted, non-draft
+/// rows — so it stays fast with a large catalogue.
+@TableIndex(name: 'idx_varieties_deleted_draft', columns: {#isDeleted, #isDraft})
 class Varieties extends Table with SyncColumns {
   TextColumn get label => text()();
   TextColumn get speciesId => text().nullable()(); // → Species
@@ -77,6 +81,10 @@ class SpeciesCommonNames extends Table with SyncColumns {
 
 /// A homogeneous batch held for a Variety — its own year and its own unit.
 /// Quantity (commons_core value type) is flattened into columns here.
+///
+/// Indexed by [varietyId] — the inventory list joins lots per variety (types,
+/// shared status, viability), so this avoids a full scan per reload.
+@TableIndex(name: 'idx_lots_variety', columns: {#varietyId})
 class Lots extends Table with SyncColumns {
   TextColumn get varietyId => text()();
   TextColumn get type =>
@@ -181,12 +189,26 @@ class Parties extends Table with SyncColumns {
 /// rest by SQLCipher) via [bytes]; external files use [uri]. Storing bytes here
 /// keeps the "no plaintext at rest" rule for photos in Block 1; an external
 /// encrypted file store is a later optimization.
+///
+/// Indexed by (parentType, parentId, kind) — the list's "first photo per
+/// variety" lookup filters on exactly these.
+@TableIndex(
+  name: 'idx_attachments_parent',
+  columns: {#parentType, #parentId, #kind},
+)
 class Attachments extends Table with SyncColumns {
   TextColumn get parentType => textEnum<ParentType>()();
   TextColumn get parentId => text()();
   TextColumn get kind => textEnum<AttachmentKind>()();
   TextColumn get uri => text().nullable()();
   BlobColumn get bytes => blob().nullable()();
+
+  /// A small JPEG thumbnail of [bytes] (photos only), decoded once on save so
+  /// the inventory list never has to decode the full-resolution photo for a
+  /// 48px avatar. Purely derived, local and regenerable — it is EXCLUDED from
+  /// CRDT sync payloads and backups (see [SyncColumns] usage); a peer or a
+  /// restored backup regenerates it lazily via `backfillThumbnails`.
+  BlobColumn get thumbnail => blob().nullable()();
   TextColumn get mimeType => text().nullable()();
 
   /// Display order among sibling attachments (lower first). The lowest-ordered