Fix bugs and improve robustness across the codebase

- Fix staged files being silently cleared when commit uses inline files
- Refactor step navigation to use direct go_to_step instead of fragile delta math
- Change step numbers from i32 to u32 (reject negative values at parse time)
- Add tour rm command to mark files for removal during carry-forward
- Add tour reset command to clear session and remove tracked files
- Consolidate duplicate recursive copy functions into shared copy_tree in utils
- Validate step directories are sequential (detect corruption)
- Detect binary files in diffs instead of showing garbage
- Use /// doc comments on enum variants so clap generates proper help text
- Remove custom Help subcommand in favor of clap's built-in --help
- Add CorruptedTour error variant for integrity checks

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

src/reset.rs

@@ -0,0 +1,18 @@
+use crate::error::TourError;
+use crate::step;
+use crate::utils::require_tour;
+use crate::SESSION_PATH;
+use std::fs;
+
+pub fn reset() -> Result<(), TourError> {
+    require_tour()?;
+
+    let cwd = std::env::current_dir()?;
+    let tracked = step::get_tracked_files()?;
+    step::remove_tracked_files(&cwd, &tracked)?;
+
+    let _ = fs::remove_file(SESSION_PATH);
+
+    println!("Tour session reset. Tracked files removed from working directory.");
+    Ok(())
+}