Rename Castle Accounting extension to Libra

Full identifier rename: module path lnbits.extensions.castle →
lnbits.extensions.libra, DB ext_castle → ext_libra, URL prefix
/castle/ → /libra/, manifest id castle → libra, fava ledger slug
default castle-ledger → libra-ledger, Beancount source metadata
castle-api → libra-api and link prefixes castle-{entry,tx}- →
libra-{entry,tx}-, column castle_wallet_id → libra_wallet_id, all
Python/JS/HTML identifiers (castle_ext, CastleSettings,
castle_reference, castleWalletConfigured, etc.).

Display name "Castle Accounting" → "Libra" (the scales/balance
metaphor — fits double-entry bookkeeping).

No backward compat: production hosts will be force-updated. Old
castle-prefixed Beancount metadata in existing Fava ledgers is
historical; new entries use libra-* prefixes going forward.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

core/validation.py

@@ -1,5 +1,5 @@
 """
-Validation rules for Castle accounting.
+Validation rules for Libra accounting.
 
 Comprehensive validation following Beancount's plugin system approach,
 but implemented as simple functions that can be called directly.
@@ -159,7 +159,7 @@ def validate_receivable_entry(
     revenue_account_type: str
 ) -> None:
     """
-    Validate a receivable entry (user owes castle).
+    Validate a receivable entry (user owes libra).
 
     Args:
         user_id: User ID