[PER-10768] Add preview placeholders for files that are still processing, can't see or failed to preview

[aasandei-vsp]

This PR adds preview placeholders for files that are still processing, can't actually be previewed or the BE failed to generate a copy for previewing. This applies mostly to docx file and such, but it also shows a nice preview page for files like archives, that we cannot actually see in the browser.

Issue: PER-10768

Click here to view curated manual test cases

# Manual test cases — record preview states (PER-10768, part 1)

The visible change: opening a record that has no viewable copy yet now shows a nice friendly screen, with and accurate message about the state of the file copy.

---

Preparing a copy ⭐

Scenario — a document straight after upload

1. Upload the .docx and open it in the viewer straight away.
   • EXPECTED: See the screen We're still preparing this file to view.
2. Click Download original.
   • EXPECTED: The original .docx downloads.
3. Click the help link.
   • EXPECTED: A page opens in a new tab, with the specified content.
4. Leave the viewer open until the copy is ready (should take a few minutes).
   • EXPECTED: The screen switches to the document preview on its own, without reloading the page.

Scenario — formats whose original the browser can't show ⭐

1. Upload the .tiff and open it straight away. --> NEEDS TESTING ON DEV
   • EXPECTED: See the screen We're still preparing this file to view.
2. Repeat with the .heic, the .avi and the .wma.
   • EXPECTED: See the screen We're still preparing this file to view.
3. Reopen the .tiff once its copy is ready.
   • EXPECTED: The image shows in the zoomable viewer.

---

Files that show from their original

(cheap regression checks: these must look exactly as before)

Scenario — opening straight after upload

1. Upload the .jpg, .mp4, .mp3 and .pdf, and open each one straight away.
   • EXPECTED: Each one shows correctly.

---

Can't show it here

Scenario — a format that never gets a copy

1. Upload the .zip and open it.
   • EXPECTED: This file is stored, but we can't show it here, with ZIP on the icon and on Download original, and the link Which files can Permanent preview?.

---

Failed copy

Scenario — an old document without a copy

(only if your archive has one) --> THIS CAN BE EASILY TESTED ON LOCAL(we don't seem to make copies there)

1. Open the .docx that is more than a day old and never got a copy.
   • EXPECTED: We couldn't make a copy of this file to view, Download original, and the link Get help with this file.

---

Moving around while a copy is being prepared

Scenario — arrows and closing

1. Open the freshly uploaded .docx from a folder that also holds the .jpg, and use the arrows to move to the .jpg.
   • EXPECTED: The image shows. No preparing screen is left behind.
2. Move back to the .docx.
   • EXPECTED: The preparing screen again, or the preview if the copy arrived in the meantime.
3. Close the viewer while the .docx is still preparing, wait a minute, and open the .jpg.
   • EXPECTED: The .jpg opens normally, with no errors.

---

Sharing

Scenario — an unlisted share link

1. Share the freshly uploaded .docx with an unlisted link, and open the link in a private window.
   • EXPECTED: The preparing screen. Once the copy is ready it switches to the preview on its own.

[codecov]

Codecov Report

❌ Patch coverage is 98.78049% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 54.72%. Comparing base (d88916a) to head (ae01846).

Files with missing lines	Patch %	Lines
...er/components/file-viewer/file-viewer.component.ts	96.55%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                                    Coverage Diff                                     @@
##           PER-10680-migrate-navigate-lean-refresh-current-folder    #1198      +/-   ##
==========================================================================================
+ Coverage                                                   54.53%   54.72%   +0.18%     
==========================================================================================
  Files                                                         368      372       +4     
  Lines                                                       12914    12990      +76     
  Branches                                                     2367     2383      +16     
==========================================================================================
+ Hits                                                         7043     7109      +66     
- Misses                                                       5634     5643       +9     
- Partials                                                      237      238       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.