fix(ui): handle auth/session errors using HTTP semantics

[VarshiniGunti]

📋 Description

JIRA ID: N/A (GitHub issue #114)

This PR updates MMU-UI to correctly consume REST-style HTTP error responses (4xx/5xx) instead of relying on side-effect navigation or opaque error objects.

What changed

1. Auth guard behavior corrected

• Updated AuthGuard.canActivate() to return explicit router-compatible values:
  • true for valid session response
  • UrlTree('/login') for invalid/expired session
• Replaced side-effect-based router.navigate() flow with map(...) return logic.
• Added catchError(...) fallback to route to login via UrlTree on HTTP errors.

2. Login error handling aligned with HTTP semantics

• Updated login error callback to process HttpErrorResponse.
• Added status-based error message mapping for:
  • 400, 401, 403, 404, 409, 500
• Preserved API-provided errorMessage when available.
• Ensures users get consistent, meaningful feedback for real HTTP failures.

Motivation

Issue #114 requires UI to handle real HTTP status codes once backend endpoints stop returning 200 for all outcomes.
This PR makes authentication/session and login flows robust against 4xx/5xx semantics and removes route activation race behavior.

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✅ Type of Change

• 🐞 Bug fix (non-breaking change which resolves an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 🔥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 🛠 Refactor (change that is neither a fix nor a new feature)
• ⚙️ Config change (configuration file or build script updates)
• 📚 Documentation (updates to docs or readme)
• 🧪 Tests (adding new or updating existing tests)
• 🎨 UI/UX (changes that affect the user interface)
• 🚀 Performance (improves performance)
• 🧹 Chore (miscellaneous changes that don't modify src or test files)

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ℹ️ Additional Information

Validation performed

• Verified canActivate now returns boolean | UrlTree and no longer depends on router.navigate() side effects.
• Verified login flow handles HttpErrorResponse and displays status-aware messages.
• Confirmed session-invalid/error paths redirect to /login consistently through guard return values.
• Kept changes intentionally scoped to auth/session and login flow to reduce regression risk.

Linked scope

• This PR is the MMU-UI half of issue #114 and pairs with the MMU-API PR that introduces proper backend HTTP status responses.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: db8e47ba-16e0-42a0-93b7-1df359411372

📥 Commits

Reviewing files that changed from the base of the PR and between 22509ad and 28c6284.

📒 Files selected for processing (2)

• src/app/app-modules/core/services/auth-guard.service.ts
• src/app/app-modules/login/login.component.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[sonarqubecloud]

Quality Gate passed

Issues
2 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