feat: add support for stat sheet SVG rendering

Introduces the ability to discover and render `*.sheet.svg` files.
These files can contain `<text>` elements with `${key}` templates
that reactively update based on the current journal stats.

- Add `StatSheet` type and CLI scanning logic
- Implement `SheetView` for rendering SVGs with live bindings
- Add `parseSheet` utility to extract template patterns from SVG
- Update file indexer to include `.svg` files

src/cli/completions/index.ts

@@ -14,6 +14,7 @@ export type {
   SparkTableCompletion,
   StatDef,
   StatTemplate,
+  StatSheet,
 } from "./types.js";
 
 /**
@@ -33,5 +34,6 @@ export function scanCompletions(
     sparkTables: blocks.sparkTables,
     stats: blocks.stats,
     statTemplates: blocks.statTemplates,
+    statSheets: blocks.statSheets,
   };
 }