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/rm.rs

@@ -0,0 +1,44 @@
+use crate::error::TourError;
+use crate::utils::require_tour;
+use std::collections::HashSet;
+use std::fs::{self, OpenOptions};
+use std::io::Write;
+use std::path::PathBuf;
+
+pub const REMOVED_PATH: &str = "./.tour/removed";
+
+pub fn rm(files: Vec<PathBuf>) -> Result<(), TourError> {
+    require_tour()?;
+
+    let existing = get_removed()?;
+    let existing_set: HashSet<PathBuf> = existing.into_iter().collect();
+
+    let mut removed_file = OpenOptions::new()
+        .append(true)
+        .create(true)
+        .open(REMOVED_PATH)?;
+
+    for file in &files {
+        if existing_set.contains(file) {
+            println!("already marked for removal: {}", file.display());
+        } else {
+            writeln!(removed_file, "{}", file.display())?;
+            println!("marked for removal: {}", file.display());
+        }
+    }
+
+    Ok(())
+}
+
+pub fn get_removed() -> Result<Vec<PathBuf>, std::io::Error> {
+    let content = fs::read_to_string(REMOVED_PATH).unwrap_or_default();
+    Ok(content
+        .lines()
+        .filter(|l| !l.is_empty())
+        .map(PathBuf::from)
+        .collect())
+}
+
+pub fn clear_removed() -> Result<(), std::io::Error> {
+    fs::write(REMOVED_PATH, "")
+}