Clean up awkward "the Libra" phrasing left over from rename

Replaces entity-sense references to "the Libra" with "the
organization"/"the collective" where Libra was being used as a
stand-in for the original "Castle" entity, and drops the redundant
"(like cooperatives)" parenthetical in DOCUMENTATION.md. Also swaps
the 🏰 emoji in the import helper for ⚖️.

Closes #12

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

README.md

@@ -30,7 +30,7 @@ Enable the extension through the LNbits admin interface or by adding it to your
    - Choose "Liability" if you want reimbursement
    - Choose "Equity" if it's a contribution
 
-2. **View Your Balance**: See if the Libra owes you money or vice versa
+2. **View Your Balance**: See if the collective owes you money or vice versa
 
 3. **Pay Outstanding Balance**: Generate a Lightning invoice to settle what you owe
 
@@ -54,8 +54,8 @@ Enable the extension through the LNbits admin interface or by adding it to your
 
 ### Account Types
 
-- **Assets**: Things the Libra owns (Cash, Bank, Accounts Receivable)
-- **Liabilities**: What the Libra owes (Accounts Payable to members)
+- **Assets**: Things the organization owns (Cash, Bank, Accounts Receivable)
+- **Liabilities**: What the organization owes (Accounts Payable to members)
 - **Equity**: Member contributions and retained earnings
 - **Revenue**: Income streams
 - **Expenses**: Operating costs