Initial implementation of duplicate finder

Full project per spec: FastAPI backend, 4-method duplicate detection
(SHA-256, phash, EXIF, filesize), Google Takeout pre-processor,
4 scan modes, and dark-theme vanilla JS gallery frontend.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

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+# Duplicate Finder
+
+A self-hosted Docker web app that scans a photo/video library, detects duplicates using four methods, and lets you review them in a gallery UI. **No files are ever moved, renamed, or deleted** — all decisions are recorded in SQLite only.
+
+## Quick start
+
+```bash
+# 1. Edit docker-compose.yml — set your photos volume path
+# 2. Build and run
+docker compose up -d --build
+# 3. Open http://localhost:8765
+# 4. Enter folder path in UI and click Scan
+```
+
+## Volume mounts
+
+| Container path | Purpose |
+|---|---|
+| `/photos` | Your photo library — mounted **read-only** |
+| `/data` | SQLite database persistence |
+
+Edit `docker-compose.yml` to point these at your NAS paths.
+
+## Detection methods
+
+| Method | Color | Description |
+|---|---|---|
+| SHA-256 | Blue | Byte-identical files |
+| Perceptual hash | Purple | Visually similar photos (hamming ≤ 10) |
+| EXIF timestamp + device | Amber | Same camera, same moment |
+| File size + dimensions | Gray | Same size and resolution (low confidence) |
+
+## Scan modes
+
+| Mode | Description |
+|---|---|
+| Incremental | Only re-hashes changed/new files. Prior decisions preserved. |
+| New files only | Indexes newly added files. Existing decisions untouched. |
+| Rebuild groups | Re-runs detection on existing index. No re-hashing. |
+| Full reset | Wipes everything and scans from scratch. |
+
+## Google Takeout
+
+The scanner automatically detects Google Takeout folder structures and reads `.json` sidecar files to restore correct capture timestamps and original filenames. Takeout files are flagged in the UI.
+
+## What "redundant" means
+
+Marking a file redundant **only writes to the database**. Nothing is moved, renamed, or deleted. This tool produces a decision record only. A separate tool handles file actions.
+
+## Tech stack
+
+- Python 3.12, FastAPI, Uvicorn
+- SQLite (stdlib `sqlite3`)
+- Pillow, imagehash, pillow-heif
+- Vanilla JS single-page frontend
+- Docker / docker-compose