Rename castle-app to libra-app

Match the upstream LNbits extension rebrand (Castle Accounting → Libra).
Renames the standalone PWA build artifacts and all references:

- castle.html → libra.html
- vite.castle.config.ts → vite.libra.config.ts (PWA name "Libra —
  Team Accounting", short_name "Libra", manifest id libra-accounting)
- npm scripts: build:castle/dev:castle/preview:castle → build:libra
  etc; dev:all and build:demo chains updated; dist-castle → dist-libra
- Hub tile: Lucide icon Castle → Scale (the scales/balance metaphor),
  label "Castle" → "Libra", env var VITE_HUB_CASTLE_URL → VITE_HUB_LIBRA_URL
- ExpensesAPI: /castle/api/v1/* → /libra/api/v1/* (matches the renamed
  LNbits extension's URL prefix)
- Feature flags VITE_CASTLE_INCOME_ENABLED/VITE_CASTLE_BUDGETS_ENABLED →
  VITE_LIBRA_*
- i18n: top-level "castle" namespace → "libra" across en/es/fr; all
  t('castle.*') usages updated
- localStorage key castle-expense-drafts → libra-expense-drafts
- nginx.conf.example: /castle/ routes + castle.<domain> redirect → libra
- Comments and identifiers: castleOwesUser → libraOwesUser, castle.api
  references in docs

Source dir src/accounting-app/ stays as-is (already feature-named, not
brand-named).

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

.env.example

@@ -58,7 +58,7 @@ VITE_MARKET_NADDR=naddr1qqjxgdp4vv6rydej943n2dny956rwwf4943xzwfc95ekyd3evenrsvrr
 # In LOCAL DEV with `npm run dev:all` use the per-app dev ports (defined
 # in the vite configs):
 #   VITE_HUB_ACTIVITIES_URL=http://localhost:5181
-#   VITE_HUB_CASTLE_URL=http://localhost:5180
+#   VITE_HUB_LIBRA_URL=http://localhost:5180
 #   VITE_HUB_WALLET_URL=http://localhost:5182
 #   VITE_HUB_CHAT_URL=http://localhost:5183
 #   VITE_HUB_FORUM_URL=http://localhost:5184
@@ -67,7 +67,7 @@ VITE_MARKET_NADDR=naddr1qqjxgdp4vv6rydej943n2dny956rwwf4943xzwfc95ekyd3evenrsvrr
 #
 # In PATH-MODE production (recommended for demo) — note the trailing slash:
 #   VITE_HUB_ACTIVITIES_URL=https://demo.example.com/activities/
-#   VITE_HUB_CASTLE_URL=https://demo.example.com/castle/
+#   VITE_HUB_LIBRA_URL=https://demo.example.com/libra/
 #   VITE_HUB_WALLET_URL=https://demo.example.com/wallet/
 #   VITE_HUB_CHAT_URL=https://demo.example.com/chat/
 #   VITE_HUB_FORUM_URL=https://demo.example.com/forum/
@@ -76,11 +76,11 @@ VITE_MARKET_NADDR=naddr1qqjxgdp4vv6rydej943n2dny956rwwf4943xzwfc95ekyd3evenrsvrr
 #
 # In SUBDOMAIN-MODE production:
 #   VITE_HUB_ACTIVITIES_URL=https://sortir.example.com
-#   VITE_HUB_CASTLE_URL=https://castle.example.com
+#   VITE_HUB_LIBRA_URL=https://libra.example.com
 #   ...etc
 # ───────────────────────────────────────────────────────────────────────
 VITE_HUB_ACTIVITIES_URL=
-VITE_HUB_CASTLE_URL=
+VITE_HUB_LIBRA_URL=
 VITE_HUB_WALLET_URL=
 VITE_HUB_CHAT_URL=
 VITE_HUB_FORUM_URL=