rebrand: rename VoiceBox to TalkBox throughout codebase

- All 'voicebox'/'Voicebox'/'VOICEBOX' strings replaced with 'talkbox'/'TalkBox'/'TALKBOX'
- Port changed from 17493 to 17494 (avoids conflict with upstream VoiceBox)
- MCP tool namespace: voicebox.* -> talkbox.*
- App bundle ID: sh.voicebox.app -> com.talkbox.app
- Binary names: voicebox-server -> talkbox-server, voicebox-mcp -> talkbox-mcp
- Docker user/group: voicebox -> talkbox
- Database: voicebox.db -> talkbox.db
- Env vars: VOICEBOX_* -> TALKBOX_*
- Asset files renamed: voicebox-logo.* -> talkbox-logo.*, etc.
- External binaries in tauri.conf.json updated to talkbox-server/talkbox-mcp

backend/pyproject.toml

@@ -1,5 +1,5 @@
 [project]
-name = "voicebox-backend"
+name = "talkbox-backend"
 version = "0.2.3"
 requires-python = ">=3.12"
 
@@ -14,7 +14,7 @@ src = ["."]
 
 # Files/dirs to skip entirely.
 extend-exclude = [
-    "voicebox-server.spec",
+    "talkbox-server.spec",
     "build_binary.py",
 ]