General: Rewrite global toast error messages with context and guidance

[az108]

Checklist

General

• I tested all changes and their related features with all corresponding user types.
• Language: I followed the guidelines for inclusive, diversity-sensitive, and appreciative language.
• I chose a title conforming to the naming conventions for pull requests.

Client

• I strictly followed the client coding and design guidelines.

Motivation and Context

Closes #1188.

The issue points out that most toast error messages in global.json were too terse to actually help the user. Concretely, 17 of them used the literal summary "Error" / "Fehler", and many details were one short sentence like "This is not a valid jobId." — no context for what action failed, no guidance for what to do next.

This PR walks the toast/error sections of global.json (EN + DE) and rewrites each message against the three-part pattern from the issue:

• Context — the summary names what failed ("Invalid job link", "Could not load application", "Email required").
• Cause — included in the detail only when it's user-relevant ("the link may be broken or the position may have been removed", "the code may be expired or incorrect").
• Guidance — every detail ends with a concrete next step ("browse available positions", "open it from your applications overview", "reload the page", "request a new code", "contact us if the problem persists").

Description

Edited only string values; every JSON key is preserved so no Angular component code needs touching.

Sections rewritten in both EN and DE:

Path	What changed
entity.toast.applyFlow.*	20 entries reworked. The 17 that had summary: "Error" / "Fehler" now have meaningful contextual summaries. Details rewritten to follow Context + (Cause) + Guidance.
entity.toast.applicationOverview.delete.error	Added "or contact us if the problem persists" guidance so a stuck delete has an escape hatch.
entity.upload.error.{upload,delete,rename}_failed	"Failed to X. Please try again." → "We couldn't X. Please [specific guidance], or contact us if the problem persists."
entity.aiExtraction.aiExtractionFailed	Now hints at a likely cause ("not a clear, readable PDF") and offers a manual fallback.
imageUpload.error.uploadFailed	Added connection-check + support fallback guidance.
reference.uploadFailed	External referees were getting "We could not save your letter. Please try again." — now also points them at the support email since they typically don't have an account to log a ticket through.

Withdraw-related toasts (entity.toast.applyFlow.applicationWithdrawn, errorWithdrawingApplication, applicationOverview.withdraw.*) were left untouched here because PR #2515 (Unsubmit / issue #1523) already rewrites them with copy specific to the new "move back to draft" semantics. Avoiding the conflict means the two PRs can land in either order.

Out of scope for this PR: toast messages outside global.json (e.g. job.json, evaluation.json, interview.json, settings.json). The issue title calls out global.json specifically as the worst offender, and bundling every i18n file would blow up the diff. Happy to follow up with per-file passes if you want.

Steps for Testing

The fastest way to eyeball the changes is to read the diff — but for live verification:

1. Open the app, navigate to Apply for a job with a deliberately bad URL like /application/creation?jobId=not-a-uuid. You should see the "Invalid job link" toast with the new wording, not the old "Error / This is not a valid jobId.".
2. Open My applications, click Edit on a submitted (non-draft) application — verify the "Application no longer editable" toast appears with the new explanatory text.
3. Try to upload an oversized document on the application page — confirm the existing size-limit toasts still trigger (they were already informative and weren't touched).
4. Switch UI language to German and repeat 1–3 to verify the German strings.

Review Progress

Code Review

• Code Review 1

Manual Tests

• Trigger an applyFlow toast in EN and read it as a user — does it actually help?
• Same in DE
• Document upload error toasts

Test Coverage

Client

Class/File	Line Coverage	Lines	Expects	Ratio
toast-service.ts	100.00%	73	10	13.7

Last updated: 2026-05-21 12:59:33 UTC

[codacy-production]

Not up to standards ⛔

🔴 Issues 1 high

Alerts:
⚠ 1 issue (≤ 0 issues of at least minor severity)

Results:
1 new issue

Category	Results
Security	1 high

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[Cathy0123456789]

Tested locally, some error messages are too long to be read within the 3 sec they pop up approximately.