fix(api): enforce HTTP status semantics for login/session endpoints

[VarshiniGunti]

📋 Description

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

This PR starts the MMU-API side of HTTP status code correction for login/session-related endpoints and introduces centralized exception handling with a standard error response structure.

What changed

1. Centralized exception handling

• Added global exception handler using @ControllerAdvice:
  • GlobalExceptionHandler
• Added standardized error payload model:
  • ApiErrorResponse with timestamp, statusCode, error, errorMessage, path

2. Login/session controller status code alignment

• Updated IemrMmuLoginController endpoints to return ResponseEntity<String> with explicit HTTP status codes instead of always returning a 200-style body.
• Applied explicit status handling:
  • 200 for success
  • 400 for invalid request payload/parameters
  • 401 for missing/invalid auth token
  • 404 for not found scenarios (getVanMaster)
  • 500 for internal server errors

3. Swagger/OpenAPI response alignment

• Added @ApiResponses annotations on updated endpoints to reflect expected HTTP responses (200/400/401/404/500), improving API contract clarity for consumers.

Motivation

Issue #114 highlights that APIs were often returning success semantics even for failure scenarios, making UI handling and debugging difficult.
This PR improves REST compliance and creates a reusable exception/status pattern that can be extended across additional controllers in follow-up work.

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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

• Ran compile check successfully:
  • mvn -DskipTests compile
• Confirmed the build succeeds with this change set.
• Existing project-wide checkstyle warnings are present in the repo baseline and are not introduced by this PR.

Notes

• This is the backend/API part of #114 and is designed to pair with the MMU-UI PR that updates UI error handling for 4xx/5xx responses.
• Scope is intentionally focused on login/session-related endpoints and centralized exception foundation to keep the PR mergeable and safe.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 261143c0-5938-49e0-b3a8-df5f776d50d0

📥 Commits

Reviewing files that changed from the base of the PR and between 2a87f0d and 2846f34.

📒 Files selected for processing (3)

• src/main/java/com/iemr/mmu/controller/login/IemrMmuLoginController.java
• src/main/java/com/iemr/mmu/utils/exception/ApiErrorResponse.java
• src/main/java/com/iemr/mmu/utils/exception/GlobalExceptionHandler.java

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[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