P3: fix(demo): show user-friendly authentication errors

[aspiers]

Summary

Translate known demo-client authentication failures into plain-language guidance instead of exposing developer-oriented wording such as instructions to check server logs.

Changes

• Map known callback and session failures to user-facing messages
• Preserve a neutral fallback for unknown failures
• Document the copy change with a changeset

Testing

• pnpm format:check
• pnpm lint
• pnpm typecheck
• pnpm test
• pnpm test:coverage

Screenshots

Before: the demo exposed provider/PAR terminology and told end users to inspect server logs.

After: the message gives an immediate retry action and a support escalation path without exposing implementation details.

Notes

• Focused extraction and review of work originally proposed in [WIP] many usability fixes (needs untangling) #165.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
epds-demo	Ready	Preview	Jul 30, 2026 3:55pm

[changeset-bot]

🦋 Changeset detected

Latest commit: d1276e0

The changes in this PR will be included in the next version bump.

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[railway-app]

🚅 Deployed to the ePDS-pr-226 environment in ePDS

Service	Status	Web	Updated (UTC)
@certified-app/demo	✅ Success (View Logs)	Web	Jul 30, 2026 at 4:19 pm
@certified-app/demo untrusted	✅ Success (View Logs)	Web	Jul 30, 2026 at 4:18 pm
@certified-app/auth-service	✅ Success (View Logs)	Web	Jul 30, 2026 at 1:42 pm
@certified-app/pds-core	✅ Success (View Logs)	Web	Jul 30, 2026 at 1:42 pm

[coveralls-official]

Coverage Report for CI Build 30559000234

Coverage increased (+0.03%) to 57.312%

Details

• Coverage increased (+0.03%) from the base build.
• Patch coverage: 2 of 2 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

---

Coverage Stats

Relevant Lines:	3071
Covered Lines:	1755
Line Coverage:	57.15%
Relevant Branches:	1914
Covered Branches:	1102
Branch Coverage:	57.58%
Branches in Coverage %:	Yes
Coverage Strength:	6.05 hits per line

---

💛 - Coveralls

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud