port habitica integration from JS to Rust

The old JS ppc repo had a working habitica integration. This ports all
that functionality into the new Rust-based marts package so it can run
natively without the Deno/JS runtime dependency.

Changes:
- habitica.rs: make api_request public, add get_tasks() and delete_task()
  convenience methods, register config opts
- c2vi/mod.rs: full rewrite implementing all 9 CLI commands (bed,
  clearTodos, listTodos, buyHealthPotion, addActionItems, skip, dumpLog,
  listDailies, printTask) with SQLite persistence via rusqlite
- lib.rs: wire c2vi module into marts exports
- ppc main.rs: register c2vi part at startup
- Cargo.toml: add rusqlite dependency with bundled feature

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

packages/marts/lib.rs

@@ -10,5 +10,10 @@ pub mod habitica;
 #[cfg(feature = "target-os")]
 pub use habitica::*;
 
+#[cfg(feature = "target-os")]
+pub mod c2vi;
+#[cfg(feature = "target-os")]
+pub use c2vi::*;
+
 pub mod js;
 pub use js::*;