refactor(renderer): move diff rendering into its own module

views.js sat at the project's 750-line limit, so the diff cap in the previous
commit pushed it over and every further change would have meant shaving
comments elsewhere. That is the file asking for decomposition, which is what the
architecture audit says to do.

Diff rendering is self-contained: the line cap, the line classifier and the
change-map illustration depend on nothing in views.js beyond ui and escapeHtml.
They now live in src/renderer/diff-view.js and are registered in index.html and
in the three renderer file lists that scan the bridge surface, so anything added
there is covered by the existing contract tests.

views.js drops from 755 to 714 lines and no source file exceeds 750 again. The
nested ternary that classified a diff line became a named function with guard
clauses on the way.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/browser/forgeflow.spec.mjs

@@ -281,6 +281,9 @@ test("a very large diff is capped instead of freezing the window", async ({ page
   });
   expect(selected, "the demo needs a repository with local changes").not.toBeNull();
   await expect(page.locator(".diff-view")).toBeVisible();
+  // Selecting a repository loads its diff asynchronously; that load would
+  // otherwise overwrite the diff injected below.
+  await expect.poll(() => page.evaluate(() => Boolean(ui.diff) && !ui.diff.startsWith("Loading"))).toBe(true);
 
   const measured = await page.evaluate(() => {
     const newline = String.fromCharCode(10);

tests/ipc-contract.test.mjs

@@ -3,7 +3,7 @@ import assert from "node:assert/strict";
 import { readFile } from "node:fs/promises";
 
 async function rendererSource() {
-  return (await Promise.all(["app.js", "views.js", "dialogs.js", "operations.js", "actions/shell.js", "actions/inventory.js", "actions/deployment-profile.js", "actions/deployment-operation.js", "actions/setup-and-settings.js", "actions/recovery.js", "actions/command.js", "events.js"].map((file) => readFile(new URL(`../src/renderer/${file}`, import.meta.url), "utf8")))).join("\n");
+  return (await Promise.all(["app.js", "diff-view.js", "views.js", "dialogs.js", "operations.js", "actions/shell.js", "actions/inventory.js", "actions/deployment-profile.js", "actions/deployment-operation.js", "actions/setup-and-settings.js", "actions/recovery.js", "actions/command.js", "events.js"].map((file) => readFile(new URL(`../src/renderer/${file}`, import.meta.url), "utf8")))).join("\n");
 }
 
 test("every preload invoke channel has a registered IPC handler", async () => {

tests/renderer-workflow.test.mjs

@@ -2,7 +2,7 @@ import test from "node:test";
 import assert from "node:assert/strict";
 import { readFile } from "node:fs/promises";
 
-const rendererFiles = ["app.js", "views.js", "dialogs.js", "operations.js", "actions/shell.js", "actions/inventory.js", "actions/deployment-profile.js", "actions/deployment-operation.js", "actions/setup-and-settings.js", "actions/recovery.js", "actions/command.js", "events.js"];
+const rendererFiles = ["app.js", "diff-view.js", "views.js", "dialogs.js", "operations.js", "actions/shell.js", "actions/inventory.js", "actions/deployment-profile.js", "actions/deployment-operation.js", "actions/setup-and-settings.js", "actions/recovery.js", "actions/command.js", "events.js"];
 async function rendererSource() {
   return (await Promise.all(rendererFiles.map((file) => readFile(new URL(`../src/renderer/${file}`, import.meta.url), "utf8")))).join("\n");
 }