Add a new error message and correct another one

[akellbl4]

• Resolve Make distinct error message on images validation errors #1005
• Fix error message about the read-only mode

[codecov]

Codecov Report

Merging #1006 (1b8e948) into master (6d4be02) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1006   +/-   ##
=======================================
  Coverage   43.98%   43.98%           
=======================================
  Files         127      127           
  Lines        2903     2903           
  Branches      662      662           
=======================================
  Hits         1277     1277           
  Misses       1613     1613           
  Partials       13       13           

Impacted Files	Coverage Δ
frontend/app/utils/errorUtils.ts	50.00% <ø> (ø)

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[github-actions]

size-limit report 📦

Path	Size
public/embed.mjs	2.25 KB (0%)
public/remark.mjs	65.39 KB (+0.09% 🔺)
public/remark.css	9.42 KB (0%)
public/last-comments.mjs	30.12 KB (+0.18% 🔺)
public/last-comments.css	5.05 KB (0%)
public/deleteme.mjs	9.76 KB (+0.51% 🔺)
public/counter.mjs	601 B (0%)