fix: Misc UX fixes

[charlesvien]

Problem

Several small UX papercuts across settings, the file viewer, tool output and toasts.

Closes #2168

Changes

1. Fix garbled initials in the settings avatar by extracting a shared unicode-aware getUserInitials util
2. Always render markdown files (remove the source/rendered toggle and markdownViewerStore)
3. Strip code fences from bash tool output in ExecuteToolView
4. Use filled WarningCircle icon for error toasts instead of an X

How did you test this?

Manually

[charlesvien]

• fix: Misc UX fixes #2157 👈 (View in Graphite)
• main

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[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/code/src/renderer/features/auth/utils/userInitials.ts:13-22
When only `last_name` is set and `first_name` is absent, the function skips the last name entirely and falls through to email-based initials (or `"U"`). A user whose profile has `{first_name: null, last_name: "Smith"}` would get letters from their email address rather than `"S"` from their name.

```suggestion
export function getUserInitials(user: UserLike | null | undefined): string {
  const first = firstLetter(user?.first_name);
  const last = firstLetter(user?.last_name);
  if (first && last) {
    return `${first}${last}`.toUpperCase();
  }
  if (first) {
    return first.toUpperCase();
  }
  if (last) {
    return last.toUpperCase();
  }
  const emailLetters = user?.email?.match(/\p{L}/gu)?.slice(0, 2).join("");
```

_{Reviews (1): Last reviewed commit: "always render markdown files" | Re-trigger Greptile}

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/code/src/renderer/features/auth/utils/userInitials.test.ts:4-89
The team prefers parameterised tests (`it.each`). The 14 individual `it()` calls here all drive the same function with different inputs and expected outputs — a textbook case for a table-driven test. The only case that warrants its own `it` is the astral-plane one, whose inline comment adds meaningful context. Collapsing the rest into `it.each` reduces repetition and makes it easier to add new edge cases.

```suggestion
describe("getUserInitials", () => {
  it.each([
    // first + last name
    [{ first_name: "Charles", last_name: "Vien" }, "CV"],
    [{ first_name: "alice", last_name: "smith" }, "AS"],
    // single name field
    [{ first_name: "Charles" }, "C"],
    [{ last_name: "Vien" }, "V"],
    // email fallback
    [{ email: "charles.v@posthog.com" }, "CH"],
    [{ email: "1234@example.com" }, "U"],
    [{ email: "1.2_charles@posthog.com" }, "CH"],
    // non-letter prefix in names
    [{ first_name: " 123Alice" }, "A"],
    // accented characters
    [{ first_name: "Émile", last_name: "Über" }, "ÉÜ"],
    // null / undefined / empty fallback to "U"
    [null, "U"],
    [undefined, "U"],
    [{ first_name: "", last_name: "", email: "" }, "U"],
    [{ first_name: "123" }, "U"],
    [{ first_name: "123", email: "456@example.com" }, "U"],
    [{ first_name: null, last_name: null, email: "charles.v@posthog.com" }, "CH"],
  ])("getUserInitials(%o) === %s", (input, expected) => {
    expect(getUserInitials(input as Parameters<typeof getUserInitials>[0])).toBe(expected);
  });

  it("handles astral-plane characters without producing lone surrogates", () => {
    // U+20BB7 ("𠮷") is encoded as a UTF-16 surrogate pair. The old
    // implementation used string[0], which returned only the high surrogate
    // and rendered as a garbled tofu char.
    expect(getUserInitials({ first_name: "𠮷田", last_name: "Smith" })).toBe(
      "𠮷S",
    );
  });
});
```

_{Reviews (2): Last reviewed commit: "address review feedback on initials and ..." | Re-trigger Greptile}