feat(api): add categories directory

[Sam-24-dev]

Summary

• Add the tenant-safe Categories directory endpoint.
• Support the bounded selectable_only filter for future Ledger category selection.

Changes

File	Change
backend/api/category_views.py	Adds read-only category list endpoint.
backend/api/urls.py	Registers /api/v1/categories/.
backend/api/tests.py	Covers authorization, tenant scope, response contract, filters, and HTTP behavior.

Testing

• python manage.py check
• python manage.py makemigrations --check --dry-run
• Full Django suite: 312 parent tests plus disposable MySQL checks
• git diff --check

Contributor checklist

• Linked an approved issue
• Added exactly one type:* label
• Conventional commit format
• No Co-Authored-By trailers

Closes #147

[Copilot]

🟢 Approval recommended

The endpoint behavior matches the linked acceptance criteria and is backed by targeted tests for authorization, tenant scoping, strict query validation, and response contract.

Pull request overview

Adds a new tenant-safe, read-only Categories directory endpoint under the existing /api/v1/ API surface, reusing workspace-context resolution and category services to ensure consistent authorization and scoping behavior.

Changes:

• Introduces GET /api/v1/categories/ with a strict, bounded selectable_only=true|false query contract.
• Registers the new route in the API URL configuration.
• Adds API tests covering auth/session expiry, workspace scoping, role-based access, projection/ordering, filter behavior, and JSON 400/405 error contracts.

File summaries

File	Description
backend/api/category_views.py	Implements the categories directory GET endpoint with strict query validation, workspace context resolution, permission checks, deterministic ordering, and JSON no-store responses.
backend/api/urls.py	Wires the new categories/ route into the /api/v1/ URL namespace.
backend/api/tests.py	Adds coverage for the new endpoint’s authz, tenant scoping, response contract, filters, and error/method handling.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0
• Review effort level: Lite

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.