chore: initialize project scaffolding and Go module

Set up the cburn project foundation:

- go.mod: Define module "cburn" targeting Go 1.24.2 with core
  dependencies — Cobra (CLI framework), Bubble Tea + Lipgloss
  (TUI), BurntSushi/toml (config), and modernc.org/sqlite (pure-Go
  SQLite for the metrics cache, no CGO required).

- go.sum: Lock all direct and transitive dependency versions for
  reproducible builds.

- main.go: Minimal entry point that delegates to cmd.Execute(),
  following the standard Cobra application pattern.

- .gitignore: Exclude the compiled binary, IDE directories (.idea/,
  .vscode/), and macOS .DS_Store files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,9 @@
+# Binary
+cburn
+
+# IDE
+.idea/
+.vscode/
+
+# OS
+.DS_Store