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/ppc/platform/os/main.rs

@@ -18,6 +18,7 @@ fn os_main(mize: &mut Mize) -> MizeResult<()> {
     marts::cli(mize)?;
     //marts::js(mize)?;
     marts::habitica(mize)?;
+    marts::c2vi(mize)?;
 
     let mut cli = mize.get_part_native::<marts::CliPart>("cli")?;