Add NextGen library: index DB, thumbnails, AI culling, and CLIP search

Builds the "indexed library" foundation and first intelligent features on
top of the organizer (sql.js index, non-destructive in-place indexing).

Phase 0 — Library index:
- sql.js (WASM SQLite) index DB; contentHash-keyed assets, resumable indexing
  (skip by path+mtime), batch persistence (chosen over native better-sqlite3
  which fails to build on Node 24 / Python 3.12)
- Library folders (in place, non-destructive) + background indexer w/ progress
- Thumbnails generated in the AI worker (canvas->webp), cached in userData;
  served via photoai-media://thumb by hash; thumbnail grid w/ pagination

Phase 1 — AI quality assessment & culling:
- Focus (Laplacian variance), exposure (histogram), eyes-open (face-api EAR)
  computed in one analyze pass alongside the thumbnail
- Culling filters (candidate/rejected) + quality badges
- Adjustable thresholds (live SQL re-classification from stored raw scores,
  no re-analysis) + manual star rating (0-5) and color labels (usermeta)

Phase 2 — CLIP natural-language / similarity search:
- @huggingface/transformers (WASM/WebGPU, no native build)
- CLIP image/text embeddings (lazy-loaded); Korean queries auto-translated
  via opus-mt-ko-en into the English CLIP
- Embeddings stored as SQLite BLOBs; "build search index" batch w/ progress;
  brute-force cosine search; new Search tab
- Note: models download from HF Hub on first use; fully-offline ORT-wasm
  packaging and KO search-accuracy tuning are follow-ups

Tabs added (Organize / Library / Search). All typecheck/tests(12)/build green;
boot smoke verified across phases.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main/settingsStore.ts

@@ -2,13 +2,14 @@ import { app } from 'electron'
 import { readFile, writeFile, mkdir } from 'node:fs/promises'
 import { join } from 'node:path'
 import type { Settings } from '@shared/types'
-import { SETTINGS_FILE } from '@shared/constants'
+import { SETTINGS_FILE, QUALITY_THRESHOLDS } from '@shared/constants'
 import { DEFAULT_LANG } from '@shared/i18n'
 
 const DEFAULTS: Settings = {
   language: DEFAULT_LANG, // 기본 한국어
   theme: 'dark', // 기본 다크모드
-  onboarded: false
+  onboarded: false,
+  qualityThresholds: { ...QUALITY_THRESHOLDS }
 }
 
 /** 앱 설정(언어/테마/온보딩) 영속화. userData/settings.json */