Error Handling when TERM variable is invalid

[cattyman919]

PR Description

Resolves #4868

The root cause stems from running an external command infocmp in setupterm function from tcell dependency.

lazygit/vendor/github.com/gdamore/tcell/v2/terminfo/dynamic/dynamic.go

Lines 119 to 130 in 0d5a410

	func (tc *termcap) setupterm(name string) error {
	cmd := exec.Command("infocmp", "-1", name)
	output := &bytes.Buffer{}
	cmd.Stdout = output
	tc.strs = make(map[string]string)
	tc.bools = make(map[string]bool)
	tc.nums = make(map[string]int)
	if err := cmd.Run(); err != nil {
	return err
	}

The error returns 'exit status 1' which will be propagate all the way up to app.go.

Unset Term Variable

Before

> unset TERM
> lazygit
Not in a git repository. Create a new git repository? (y/N): N
2025/09/07 18:52:22 An error occurred! Please create an issue at: https://github.com/jesseduffield/lazygit/issues

*fmt.wrapError terminal entry not found: term not set
/home/runner/work/lazygit/lazygit/pkg/app/app.go:55 (0xc9d2bf)
/home/runner/work/lazygit/lazygit/pkg/app/entry_point.go:172 (0xc9f486)
/home/runner/work/lazygit/lazygit/main.go:23 (0xca0838)
/opt/hostedtoolcache/go/1.24.5/x64/src/internal/runtime/atomic/types.go:194 (0x443f6b)
/opt/hostedtoolcache/go/1.24.5/x64/src/runtime/asm_amd64.s:1700 (0x480ca1)

After

> unset TERM
> lazygit
Not in a git repository. Create a new git repository? (y/N): N
2025/09/07 20:58:03 Error: TERM environment variable not set.
exit status 1

Invalid Term Variable

Before

> export TERM=skibidi
> lazygit
Not in a git repository. Create a new git repository? (y/N): N
2025/09/07 18:49:56 An error occurred! Please create an issue at: https://github.com/jesseduffield/lazygit/issues

*exec.ExitError exit status 1
/home/runner/work/lazygit/lazygit/pkg/app/app.go:55 (0xc9d2bf)
/home/runner/work/lazygit/lazygit/pkg/app/entry_point.go:172 (0xc9f486)
/home/runner/work/lazygit/lazygit/main.go:23 (0xca0838)
/opt/hostedtoolcache/go/1.24.5/x64/src/internal/runtime/atomic/types.go:194 (0x443f6b)
/opt/hostedtoolcache/go/1.24.5/x64/src/runtime/asm_amd64.s:1700 (0x480ca1)

After

> export TERM=skibidi
> lazygit
2025/09/07 21:00:01 Error: could not find terminal info for $TERM 'skibidi'. Please check your TERM variable is set correctly.
exit status 1

Please check if the PR fulfills these requirements

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• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc