Add MoonBit CI, core module tests, and fix all moon check warnings

• Add .github/workflows/ci.yml running moon check and moon test on push/PR
• Add unit tests for Timer/HabitTracker (app/app_test.mbt) and TUI rendering/layout/ANSI helpers (tui/tui_test.mbt)
• Fix 54 moon check warnings: deprecated not() and .lsr(), redundant pub modifiers, unused variables, missing priv markers
• Fix pre-existing sha256/md5 padding bug: length bytes written with shifts >= 32 wrapped mod 32, corrupting the padded block; add known-answer tests for both hashes
• Render the title text in the TUI header instead of dropping it