fix: add empty state fallback for unanalyzed tabs

[Medora140]

Description

Implemented proper empty-state handling for result tabs to prevent infinite loading skeletons before analysis is executed.

Users now receive clear fallback messages when switching between Explain, Debug, and Improve tabs without running analysis first.

Related Issue

Fixes #263

Type of change

• Bug fix
• New feature / enhancement
• Documentation update
• Test addition
• Refactor

Checklist

• I have read CONTRIBUTING.md
• My branch is up to date with main
• I have run pytest -v and all tests pass
• I have not introduced duplicate issues or features
• My PR title follows the format: feat/fix/docs/test: short description
• I have added tests for new features (Level 2 and 3 issues)
• No hardcoded secrets or API keys in my code
• This PR is linked to a GSSoC 2026 issue

Screenshots (if frontend change)

Before

• Debug and Improve tabs displayed endless loading skeletons
• Empty panels appeared stuck before analysis
• No guidance was shown to users

After

• Proper empty-state messages are displayed instantly
• Tabs guide users to run analysis first
• Infinite loading placeholders are removed
• Result tab UX is more consistent and accessible

Test evidence

pytest -v
============================== test session starts ===============================
platform win32 -- Python 3.12.4, pytest-9.0.3, pluggy-1.6.0 -- C:\Users\Medora Gomes\Desktop\GSSOC\AI-dev-assistant2\AI-dev-assistant\venv\Scripts\python.exe
cachedir: .pytest_cache
rootdir: C:\Users\Medora Gomes\Desktop\GSSOC\AI-dev-assistant2\AI-dev-assistant
plugins: anyio-4.13.0, asyncio-1.3.0
asyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
collected 126 items                                                               

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============================== 126 passed in 9.54s ===============================

[Medora140]

Hi @imDarshanGK , All merge conflicts have been resolved. Please let me know if any changes are needed.

[imDarshanGK]

@Medora140 update your branch with the latest main changes and resolve conflicts