feat: ledger-gui — a read-only, live desktop view of the books

egui/wgpu app for owners and their accountant: Overview, Cash, Profit,
Transactions (with rendered receipts and journal history), Reports
(statements with interval columns, comparisons, drill-down), Accounts,
Documents, Company, Journal; Ctrl+K palette; back/forward; light/dark.
Follows the journal live (~30 ms from write to screen). --demo opens a
deterministic demo company, also used for screenshot tests.

Engine: ledger-store Snapshot (read-only, incremental, tolerant of a
half-written tail); ledger-core analysis (intervals, balance series,
P&L by interval, cash flows); ledger-config extracted from ledger-mcp
with the full company profile and cash_accounts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MtYEaR6M6Ybdhm6X98BWNu

crates/ledger-store/src/blob.rs

@@ -25,6 +25,14 @@ impl BlobStore {
         })
     }
 
+    /// Open an existing blob store for reading, creating nothing. A
+    /// missing directory just means no blobs yet.
+    pub fn open_read_only(root: &Path) -> Self {
+        Self {
+            root: root.to_path_buf(),
+        }
+    }
+
     fn path_for(&self, sha_hex: &str) -> PathBuf {
         self.root
             .join(&sha_hex[0..2])