Feat/create protected dashboard shell

[AAdewunmi]

Summary

Create the authenticated dashboard shell as the first post-login product surface for StudyBuddy.

Changes

• Added protected dashboard routing at /dashboard/.
• Added dashboard app wiring with dashboard:index.
• Rendered the dashboard through templates/dashboard/index.html.
• Connected signup and login redirects to the dashboard.
• Added a StudyBuddy-aligned dashboard layout using the current base template and theme system.
• Displayed placeholder study metrics, empty session state, account access, and role-aware messaging.

Behavior

• Anonymous users are redirected to login before accessing the dashboard.
• Authenticated users land on /dashboard/ after signup or login.
• Dashboard displays a credible Sprint 1 product shell before Sprint 2 adds study-session data.
• Existing navigation and footer remain consistent across templates.

Why

This gives users a real post-login destination and establishes the protected product surface that future study sessions, notes, goals, and progress metrics can build on.

Validation

• Django system check passed.
• Black passed.
• Ruff passed.
• Focused auth/view tests passed.
• Full test suite passed.

Result

The authentication journey now resolves into a protected dashboard shell that is aligned with the current StudyBuddy design system and ready for Sprint 2 product data.

Notes

• The dashboard is intentionally a shell for Sprint 1.
• Study-session creation, real metrics, notes, and progress data are deferred to Sprint 2.
• The dashboard uses the existing theme.css design system rather than introducing a separate Bootstrap-only layout.
• Role display is wired through studybuddy_roles, matching the current role model relationship.
• No inactive “Add Session” route is exposed until the study-session workflow exists.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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