Chat markdown content does not render right-to-left for RTL locales (Persian, Arabic)

### Self Checks

- [x] I have read the Contributing Guide and Language Policy.
- [x] This is only for bug report.
- [x] I have searched for existing issues, including closed ones.
- [x] I confirm that I am using English to submit this report.

### Dify version

1.17.0 (main)

### Cloud or Self Hosted

Self Hosted (Source)

### Steps to reproduce

1. Set the account's interface language to a right-to-left locale that Dify already ships translations for, e.g. Farsi (`fa-IR`) or Arabic (`ar-TN`), via Account Settings → Preferences → Language.
2. Open any Chat/Agent/Chatflow app and send a message in that language.
3. Observe the rendered question and answer bubbles.

### Expected Behavior

Chat message content (both the user's question and the assistant's answer) should render right-to-left, matching the natural reading direction of the selected locale — text alignment, list markers, and blockquote borders should mirror accordingly.

### Actual Behavior

Message content always renders left-to-right regardless of the active locale. The shared `Markdown` component (`web/app/components/base/markdown/index.tsx`), which renders both question and answer bubbles, never sets a `dir` attribute, so RTL-locale content displays with left-aligned, LTR-ordered text — this makes RTL conversations hard to read. This affects every RTL locale Dify currently ships translations for, not just one language.