Add ruff linter/formatter for Python

- Add ruff as dev dependency
- Configure ruff in pyproject.toml with strict 88-char line limit
- Ignore B008 (FastAPI Depends pattern is standard)
- Allow longer lines in tests for readability
- Fix all lint issues in source files
- Add Makefile targets: lint-backend, format-backend, fix-backend

backend/validation.py

@@ -1,9 +1,10 @@
 """Validation utilities for user profile fields."""
+
 import json
 from pathlib import Path
 
-from email_validator import validate_email, EmailNotValidError
 from bech32 import bech32_decode
+from email_validator import EmailNotValidError, validate_email
 
 # Load validation rules from shared constants
 _constants_path = Path(__file__).parent.parent / "shared" / "constants.json"
@@ -18,13 +19,13 @@ NPUB_RULES = _constants["validation"]["nostrNpub"]
 def validate_contact_email(value: str | None) -> str | None:
     """
     Validate contact email format.
-    
+
     Returns None if valid, error message if invalid.
     Empty/None values are valid (field is optional).
     """
     if not value:
         return None
-    
+
     try:
         validate_email(value, check_deliverability=False)
         return None
@@ -35,84 +36,84 @@ def validate_contact_email(value: str | None) -> str | None:
 def validate_telegram(value: str | None) -> str | None:
     """
     Validate Telegram handle.
-    
+
     Must start with @ if provided, with characters after @ within max length.
     Returns None if valid, error message if invalid.
     Empty/None values are valid (field is optional).
     """
     if not value:
         return None
-    
+
     prefix = TELEGRAM_RULES["mustStartWith"]
     max_len = TELEGRAM_RULES["maxLengthAfterAt"]
-    
+
     if not value.startswith(prefix):
         return f"Telegram handle must start with {prefix}"
-    
+
     handle = value[1:]
     if not handle:
         return f"Telegram handle must have at least one character after {prefix}"
-    
+
     if len(handle) > max_len:
         return f"Telegram handle must be at most {max_len} characters (after {prefix})"
-    
+
     return None
 
 
 def validate_signal(value: str | None) -> str | None:
     """
     Validate Signal username.
-    
+
     Any non-empty string within max length is valid.
     Returns None if valid, error message if invalid.
     Empty/None values are valid (field is optional).
     """
     if not value:
         return None
-    
+
     max_len = SIGNAL_RULES["maxLength"]
-    
+
     # Signal usernames are fairly permissive, just check it's not empty
     if len(value.strip()) == 0:
         return "Signal username cannot be empty"
-    
+
     if len(value) > max_len:
         return f"Signal username must be at most {max_len} characters"
-    
+
     return None
 
 
 def validate_nostr_npub(value: str | None) -> str | None:
     """
     Validate Nostr npub (public key in bech32 format).
-    
+
     Must be valid bech32 with 'npub' prefix.
     Returns None if valid, error message if invalid.
     Empty/None values are valid (field is optional).
     """
     if not value:
         return None
-    
+
     prefix = NPUB_RULES["prefix"]
     expected_words = NPUB_RULES["bech32Words"]
-    
+
     if not value.startswith(prefix):
         return f"Nostr npub must start with '{prefix}'"
-    
+
     # Decode bech32 to validate checksum
     hrp, data = bech32_decode(value)
-    
+
     if hrp is None or data is None:
         return "Invalid Nostr npub: bech32 checksum failed"
-    
+
     if hrp != "npub":
         return "Nostr npub must have 'npub' prefix"
-    
+
     # npub should decode to 32 bytes (256 bits) for a public key
     # In bech32, each character encodes 5 bits, so 32 bytes = 52 characters of data
     if len(data) != expected_words:
         return "Invalid Nostr npub: incorrect length"
-    
+
     return None
 
 
@@ -124,23 +125,22 @@ def validate_profile_fields(
 ) -> dict[str, str]:
     """
     Validate all profile fields at once.
-    
+
     Returns a dict of field_name -> error_message for any invalid fields.
     Empty dict means all fields are valid.
     """
     errors: dict[str, str] = {}
-    
+
     if err := validate_contact_email(contact_email):
         errors["contact_email"] = err
-    
+
     if err := validate_telegram(telegram):
         errors["telegram"] = err
-    
+
     if err := validate_signal(signal):
         errors["signal"] = err
-    
+
     if err := validate_nostr_npub(nostr_npub):
         errors["nostr_npub"] = err
-    
-    return errors
 
+    return errors