fix(attribution): parse binary diffs, source generator from model, sync schema $version

Three follow-up review items from Copilot:

- parseDiffStat now handles git's binary-diff format (`path | Bin A ->
  B bytes`) using the byte delta with a floor of 1. Without this,
  binary edits arrived at the attribution payload as diffSize=0 and
  were silently dropped. Also extracted the parser to a top-level
  exported function so the binary path is unit-testable; added five
  targeted cases (text/binary/rename normalisation/summary skip).

- attachCommitAttribution now passes `this.config.getModel()` into
  generateNotePayload instead of the user-configurable
  `gitCoAuthor.name`. The note's `generator` field reflects which
  model produced the changes — and CommitAttributionService's
  sanitizeModelName() actually has the codename to scrub now.

- generate-settings-schema.ts imports SETTINGS_VERSION instead of
  hardcoding `default: 3`, so a future bump propagates to the emitted
  JSON schema in one place. Regenerated settings.schema.json bumps
  $version's default from 3 to 4 to match the V4 migration.

scripts/generate-settings-schema.ts

@@ -25,6 +25,7 @@ import type {
   SettingsSchema,
 } from '../packages/cli/src/config/settingsSchema.js';
 import { getSettingsSchema } from '../packages/cli/src/config/settingsSchema.js';
+import { SETTINGS_VERSION } from '../packages/cli/src/config/settings.js';
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
@@ -194,11 +195,12 @@ function generateJsonSchema(
     );
   }
 
-  // Add $version property
+  // Add $version property — sourced from settings.ts so a SETTINGS_VERSION
+  // bump propagates here instead of needing a parallel manual edit.
   jsonSchema.properties!['$version'] = {
     type: 'number',
     description: 'Settings schema version for migration tracking.',
-    default: 3,
+    default: SETTINGS_VERSION,
   };
 
   return jsonSchema;