make form available after failed commit sending

[akellbl4]

Resolves #965

• add a new error code on the server for proper indication on the frontend
• simplify errors map on the frontend in favor of simple and small code

[codecov]

Codecov Report

Merging #981 (59d6499) into master (82f8f6c) will decrease coverage by 0.02%.
The diff coverage is 63.63%.

@@            Coverage Diff             @@
##           master     #981      +/-   ##
==========================================
- Coverage   43.17%   43.14%   -0.03%     
==========================================
  Files         127      127              
  Lines        2622     2612      -10     
  Branches      519      514       -5     
==========================================
- Hits         1132     1127       -5     
+ Misses       1444     1439       -5     
  Partials       46       46              

Impacted Files	Coverage Δ
...ntend/app/components/comment-form/comment-form.tsx	46.44% <ø> (ø)
frontend/app/utils/errorUtils.ts	50.00% <40.00%> (ø)
frontend/app/common/fetcher.ts	94.64% <83.33%> (ø)

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[github-actions]

size-limit report 📦

Path	Size
public/embed.mjs	2.28 KB (0%)
public/remark.mjs	67.18 KB (-0.29% 🔽)
public/remark.css	10.62 KB (0%)
public/last-comments.mjs	30.91 KB (-0.6% 🔽)
public/last-comments.css	5.76 KB (0%)
public/deleteme.mjs	9.96 KB (-1.51% 🔽)
public/counter.mjs	626 B (0%)

[coveralls]

Pull Request Test Coverage Report for Build 814863324

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 83.564%

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Totals
Change from base Build 812645973:	0.0%
Covered Lines:	5364
Relevant Lines:	6419

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💛 - Coveralls

[umputun]

backend change makes sense