chore(gui-test): implement vulture tool to detect dead code and remove those dead code

[Asmitapaudel]

Part of #553

Vulture is a static code analyzer that finds unused/dead code in Python projects.

Add vulture to the lint dependency group for dead code detection.

Confidence levels:

• 100% → definitely unused
• 80% → pretty sure unused
• 60% → might be unused (noisy, not recommended)

Using min-confidence = 80 to avoid false positives.

Commands to scan by category:

# unused variables
uv run vulture . | grep "unused variable"

# unused imports
uv run vulture . | grep "unused import"

# unused functions
uv run vulture . | grep "unused function"

# unused classes
uv run vulture . | grep "unused class"

# all at once
uv run vulture .

Since the codebase had minimal dead code after running vulture, all categories (variables, imports, functions, classes) are cleaned up in this single PR instead of splitting across multiple PRs.

[saw-jan]

@Asmitapaudel let's keep this as it is for now. we will sort out the test code lint setup and rules first and then we can come to this.