feat: GenAI Shortcuts for PromptInput

[ernst-dev]

Description

Adds shortcuts features to PromptInput:

• Underlying input becomes a div with contenteditable enabled to allow rendering custom elements
• Adds menu system to attach to triggers with filters @ or /
• Complex rendering logic to ensure cross-browser consistency
• Reference representation through inline Token elements

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

❌ Patch coverage is 96.40174% with 91 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.35%. Comparing base (a6cdcd0) to head (392a014).

Files with missing lines	Patch %	Lines
src/prompt-input/tokens/use-token-mode.ts	92.09%	43 Missing ⚠️
src/prompt-input/core/event-handlers.ts	96.27%	17 Missing ⚠️
src/prompt-input/core/caret-controller.ts	95.62%	16 Missing ⚠️
src/prompt-input/internal.tsx	95.68%	5 Missing ⚠️
src/prompt-input/components/token-mode.tsx	90.62%	3 Missing ⚠️
src/prompt-input/core/dom-utils.ts	98.27%	2 Missing ⚠️
src/prompt-input/core/trigger-utils.ts	98.56%	2 Missing ⚠️
src/prompt-input/components/menu-dropdown.tsx	94.44%	1 Missing ⚠️
src/prompt-input/core/token-utils.ts	99.28%	1 Missing ⚠️
...prompt-input/utils/insert-text-content-editable.ts	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4107      +/-   ##
==========================================
- Coverage   97.45%   97.35%   -0.10%     
==========================================
  Files         909      925      +16     
  Lines       26637    29116    +2479     
  Branches     9614    10530     +916     
==========================================
+ Hits        25958    28346    +2388     
- Misses        673      764      +91     
  Partials        6        6              

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[jperals]

These two strings should not change. Instead, i18nStrings.datePlaceholder should be changed to AAAA/MM/GG

[jperals]

Same as in Italian, these two strings should not have been change, it is the previous one that was wrong.

We can address existing issues separately but let's not introduce regressions.

[jperals]

Similar feedback here as with French and Italian below