fix: sidebar shows OpenCode instead of Altimate Code after upstream merge

[anandgupta42]

What does this PR do?

Fixes sidebar footer branding that was reverted to "OpenCode" by an upstream merge, and adds guards to prevent it from happening again.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Issue for this PR

Closes #167

How did you verify your code works?

• Ran bun test test/branding/upstream-merge-guard.test.ts — all 87 tests pass (including 2 new TUI branding tests)
• Typecheck passes cleanly

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• New and existing unit tests pass locally with my changes

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Summary

• Replace <b>Open</b><b>Code</b> with <b>Altimate</b><b> Code</b> in sidebar footer
• Add altimate_change markers around the branding block so the upstream merge script preserves it
• Add TUI branding guard tests to upstream-merge-guard.test.ts to catch regressions
• Fix pre-existing typecheck error in training test (stale accepted/rejected properties)

Test plan

• Branding guard tests pass (87/87)
• Typecheck passes
• Visual verification: sidebar shows "Altimate Code vX.Y.Z"

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