refactor: Phase 0 — extract utils.py and providers.py, centralize provider dispatch

- Create utils.py: normalize_name, get_file_hash, safe_log_data
- Create providers.py: PROVIDER_REGISTRY with get_default_endpoint,
  get_default_model, build_auth_headers
- Add DEFAULT_ANTHROPIC_MODEL constant (was incorrectly using gpt-4o-mini)
- Replace all inline dispatch tables in config_flow.py and __init__.py
- Fix circular import: coordinator.py now imports from utils, not config_flow
- Fix NameError in error paths: replace bare constant refs with provider functions
- Raise ValueError for unknown providers instead of silent OpenAI fallback

custom_components/ha_text_ai/utils.py

@@ -0,0 +1,36 @@
+"""
+Utility functions for HA Text AI integration.
+
+@license: CC BY-NC-SA 4.0 International
+@author: SMKRV
+@github: https://github.com/smkrv/ha-text-ai
+@source: https://github.com/smkrv/ha-text-ai
+"""
+import hashlib
+from typing import Any
+
+from homeassistant.const import CONF_API_KEY
+
+
+def normalize_name(name: str) -> str:
+    """Normalize name to conform to HA naming convention using underscores."""
+    normalized = ''.join(c if c.isalnum() or c == '_' else '_' for c in name)
+    normalized = '_'.join(filter(None, normalized.split('_')))
+    return normalized.lower()
+
+
+def get_file_hash(file_path: str) -> str:
+    """Calculate SHA256 hash of file."""
+    sha256_hash = hashlib.sha256()
+    with open(file_path, "rb") as f:
+        for byte_block in iter(lambda: f.read(4096), b""):
+            sha256_hash.update(byte_block)
+    return sha256_hash.hexdigest()
+
+
+def safe_log_data(
+    data: dict[str, Any],
+    sensitive_keys: tuple[str, ...] = (CONF_API_KEY,),
+) -> dict[str, Any]:
+    """Filter sensitive keys from data for safe logging."""
+    return {k: "***" if k in sensitive_keys else v for k, v in data.items()}