refactor: consolidate blockchain explorer into single app and update backup ignore patterns

- Remove standalone explorer-web app (README, HTML, package files)
- Add /web endpoint to blockchain-explorer for web interface access
- Update .gitignore to exclude application backup archives (*.tar.gz, *.zip)
- Add backup documentation files to .gitignore (BACKUP_INDEX.md, README.md)
- Consolidate explorer functionality into main blockchain-explorer application

apps/wallet/src/app/settings.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from pydantic import Field, field_validator
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    """Runtime configuration for the wallet daemon service."""
+
+    app_name: str = Field(default="AITBC Wallet Daemon")
+    debug: bool = Field(default=False)
+
+    coordinator_base_url: str = Field(default="http://localhost:8011", alias="COORDINATOR_BASE_URL")
+    coordinator_api_key: str = Field(..., alias="COORDINATOR_API_KEY")
+
+    rest_prefix: str = Field(default="/v1", alias="REST_PREFIX")
+    ledger_db_path: Path = Field(default=Path("./data/wallet_ledger.db"), alias="LEDGER_DB_PATH")
+
+    @field_validator('coordinator_api_key')
+    @classmethod
+    def validate_api_key(cls, v: str) -> str:
+        if v.startswith('$') or not v or v == 'your_api_key_here':
+            raise ValueError('COORDINATOR_API_KEY must be set to a valid value and cannot be a template placeholder')
+        return v
+
+    class Config:
+        env_file = ".env"
+        case_sensitive = False
+
+
+settings = Settings()