feat: Support client-side rendering for PPTX and PPT files

[spider-yamet]

Related Issue

Closes #1339

Description

This PR adds client-side rendering for PPTX (and PPT) files in the Agent Folder, as requested in #1339.

What changed:

• Data path: Main process exposes getFileAsDataUrl(path, type?) (in FileReader) so the renderer receives raw PPTX bytes as a data URL. Remote URLs are downloaded to a temp path first, then read and returned as a data URL.
• IPC: New get-file-dataurl handler and getFileAsDataUrl on electronAPI; preload and electron.d.ts updated.
• Viewer: New PptxViewer component (lazy-loaded) that decodes the data URL, parses the PPTX in the renderer with JSZip and the browser’s DOMParser, and renders slides with a filmstrip and prev/next controls.
• Folder flow: When a user selects a PPTX file, the app calls get-file-dataurl instead of open-file; content area shows PptxViewer when content is a data URL. If IPC is unavailable (e.g. browser-only), a short message explains that PPTX preview is available in the desktop app.
• Dependency: Added jszip for browser-safe PPTX unzip in the renderer.

Why: Preview was previously done in the main process (text-only HTML). Moving to client-side rendering matches the PDF pattern (raw bytes → renderer), supports remote files via the same path, and allows a proper slide-by-slide UI. Legacy .ppt is out of scope for this change.

Testing Evidence (REQUIRED)

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.
• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline

[spider-yamet]

PPT file

PPT renderer

[spider-yamet]

Please review my PR, @bytecii , @Wendong-Fan

[spider-yamet]

@bytecii @Wendong-Fan could you please review this PR?

[spider-yamet]

@bytecii @Wendong-Fan could you please review this PR?

[spider-yamet]

@fengju0213 could you please review this pr?

[4pmtong]

Thanks @spider-yamet for your contribution and your patience! Sorry for the delayed response — I'll do a detailed code review next and will follow up soon.