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>

docs/PERMISSIONS-SYSTEM.md

@@ -1,4 +1,4 @@
-# Castle Permissions System - Overview & Administration Guide
+# Libra Permissions System - Overview & Administration Guide
 
 **Date**: November 10, 2025
 **Status**: 📚 **Documentation** + 🔧 **Improvement Recommendations**
@@ -7,7 +7,7 @@
 
 ## Executive Summary
 
-Castle implements a **granular, hierarchical permission system** that controls who can access which accounts and perform what actions. The system supports permission inheritance, making it easy to grant access to entire account hierarchies with a single permission.
+Libra implements a **granular, hierarchical permission system** that controls who can access which accounts and perform what actions. The system supports permission inheritance, making it easy to grant access to entire account hierarchies with a single permission.
 
 **Key Features:**
 - ✅ **Three permission levels**: READ, SUBMIT_EXPENSE, MANAGE
@@ -680,7 +680,7 @@ CREATE TABLE account_permissions (
     expires_at TIMESTAMP,
     notes TEXT,
 
-    FOREIGN KEY (account_id) REFERENCES castle_accounts (id)
+    FOREIGN KEY (account_id) REFERENCES libra_accounts (id)
 );
 
 CREATE INDEX idx_account_permissions_user_id ON account_permissions (user_id);
@@ -840,7 +840,7 @@ async def test_expense_submission_without_permission():
 
 ## Summary
 
-The Castle permissions system is **well-designed** with strong features:
+The Libra permissions system is **well-designed** with strong features:
 - Hierarchical inheritance reduces admin burden
 - Caching provides good performance
 - Expiration and audit trail support compliance