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/SATS-EQUIVALENT-METADATA.md

@@ -8,21 +8,21 @@
 
 ## Overview
 
-The `sats-equivalent` metadata field is Castle's solution for **dual-currency tracking** in a fiat-denominated ledger. It preserves Bitcoin (satoshi) amounts alongside fiat currency amounts without violating accounting principles or creating multi-currency complexity in position balances.
+The `sats-equivalent` metadata field is Libra's solution for **dual-currency tracking** in a fiat-denominated ledger. It preserves Bitcoin (satoshi) amounts alongside fiat currency amounts without violating accounting principles or creating multi-currency complexity in position balances.
 
 ### Quick Summary
 
 - **Purpose**: Track Bitcoin/Lightning amounts in a EUR-denominated ledger
 - **Location**: Beancount posting metadata (not position amounts)
 - **Format**: String containing absolute satoshi amount (e.g., `"337096"`)
-- **Primary Use**: Calculate user balances in satoshis (Castle's primary currency)
+- **Primary Use**: Calculate user balances in satoshis (Libra's primary currency)
 - **Key Principle**: Satoshis are for reference; EUR is the actual transaction currency
 
 ---
 
 ## The Problem: Dual-Currency Tracking
 
-Castle needs to track both:
+Libra needs to track both:
 1. **Fiat amounts** (EUR, USD) - The actual transaction currency
 2. **Bitcoin amounts** (satoshis) - The Lightning Network settlement currency
 
@@ -34,7 +34,7 @@ Castle needs to track both:
 - ❌ Complicate traditional accounting reconciliation
 - ❌ Make fiat-based reporting difficult
 
-**Castle's Philosophy**: Record transactions in their **actual currency**, with Bitcoin as supplementary data.
+**Libra's Philosophy**: Record transactions in their **actual currency**, with Bitcoin as supplementary data.
 
 ---
 
@@ -88,7 +88,7 @@ if fiat_currency and fiat_amount:
 
 ### Primary Use Case: User Balances
 
-Castle's core function is tracking **who owes whom** in satoshis. The `sats-equivalent` metadata enables this.
+Libra's core function is tracking **who owes whom** in satoshis. The `sats-equivalent` metadata enables this.
 
 **Flow** (`fava_client.py:220-248`):
 
@@ -147,7 +147,7 @@ SELECT account, sum(meta["sats-equivalent"]) WHERE account ~ 'User-5987ae95'
 -- Error: BQL cannot access metadata
 ```
 
-### Why Castle Accepts This Trade-off
+### Why Libra Accepts This Trade-off
 
 **Performance Analysis** (see `docs/BQL-BALANCE-QUERIES.md`):
 1. **Caching solves the bottleneck**: 60-80% performance improvement from caching account/permission lookups
@@ -196,9 +196,9 @@ See `docs/BQL-PRICE-NOTATION-SOLUTION.md` for full analysis.
 
 **User Action**: "I paid €36.93 cash for groceries"
 
-**Castle's Internal Representation**:
+**Libra's Internal Representation**:
 ```python
-# User provides or Castle calculates:
+# User provides or Libra calculates:
 fiat_amount = Decimal("36.93")  # EUR
 fiat_currency = "EUR"
 amount_sats = 39669  # Calculated from exchange rate
@@ -232,16 +232,16 @@ line = CreateEntryLine(
 #   - Apply sign: -36.93 is negative → sats = -39669
 #   - Accumulate: user_balance_sats += -39669
 
-# Result: negative balance = Castle owes user
+# Result: negative balance = Libra owes user
 ```
 
 **User Balance Response**:
 ```json
 {
   "user_id": "5987ae95",
-  "balance": -39669,  // Castle owes user 39,669 sats
+  "balance": -39669,  // Libra owes user 39,669 sats
   "fiat_balances": {
-    "EUR": "-36.93"   // Castle owes user €36.93
+    "EUR": "-36.93"   // Libra owes user €36.93
   }
 }
 ```
@@ -306,7 +306,7 @@ The `sats-equivalent` is the **exact satoshi amount at transaction time**. It do
 
 ### 3. Separate Fiat and Sats Balances
 
-Castle tracks TWO independent balances:
+Libra tracks TWO independent balances:
 - **Satoshi balance**: Sum of `sats-equivalent` metadata (primary)
 - **Fiat balances**: Sum of EUR/USD position amounts (secondary)