fix: repair file_handlers.ts backtick escaping; update README

file_handlers.ts had AI-generated escaped backticks (\`) and template
literal dollar signs (\${) throughout, causing TypeScript compile errors
("Invalid character", "Unterminated template literal"). Fixed all 15
affected lines.

README updated: corrected seed config path from resources/seed_config.json
to ~/seed.json (external to app bundle by design), added explanation of
why it's kept external (no re-signing needed per device), and documented
the 2-char hash prefix cache layout with consistency warning.

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

README.md

@@ -12,10 +12,16 @@ This application serves as the "Native Mode" runtime for Aether podiums and devi
 
 ## ⚙️ Configuration
 
-The application requires a `seed_config.json` file to identify the device and connect to the Aether API.
+The application requires a `seed.json` file to identify the device and connect to the Aether API.
 
 ### 1. Seed Configuration
-Create/edit `resources/seed_config.json`:
+
+**Location: `~/seed.json`** (user's home directory — external to the app bundle by design)
+
+This file is intentionally kept outside the application bundle so it can be edited per-device
+without re-signing or repackaging the app. On macOS this is `/Users/<username>/seed.json`.
+
+Create/edit `~/seed.json`:
 ```json
 {
   "event_device_id": "YOUR_DEVICE_ID",
@@ -25,13 +31,30 @@ Create/edit `resources/seed_config.json`:
 }
 ```
 
-### 2. Environment Setup
+> **Note:** The `event_device_id` and `aether_api_key` values come from the Aether admin panel
+> (Events → Devices). Each physical device gets its own record and key.
+
+### 2. Development Setup
 ```bash
 npm install
-npm run build
-npm start
+npm start        # Compiles TypeScript (tsc) then launches Electron
 ```
 
+### 3. File Cache Layout
+
+Presentation files are cached locally under `hash_prefix_length`-char subdirectories (default: 2):
+```text
+[local_file_cache_path]/
+  4a/
+    4a228ef8ac1a...sha256hash...file
+  1d/
+    1d720916a831...sha256hash...file
+```
+
+**Important:** `hash_prefix_length` must be consistent. If it changes, files in old directories
+become orphaned and will be re-downloaded. The default is `2` and should not be changed unless
+explicitly coordinated across all devices.
+
 ## 🌉 The Native Bridge (`aetherNative`)
 
 The bridge is exposed to the renderer via `contextBridge`. It can be accessed in the web UI via `window.aetherNative`.