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/error.rs

@@ -2,33 +2,53 @@ use std::io;
 use std::path::PathBuf;
 
 #[derive(Debug)]
-pub enum CommitError {
-    NotADescendantOfCurrentDir(PathBuf),
-    InsideTourDir(PathBuf),
+pub enum TourError {
+    NoTour,
+    TourAlreadyExists,
+    TourEnded,
     NothingToCommit,
+    NoSteps,
+    NotADescendant(PathBuf),
+    InsideTourDir(PathBuf),
+    FileNotFound(PathBuf),
+    StepOutOfRange { step: u32, total: u32 },
+    CorruptedTour(String),
     Io(io::Error),
 }
 
-impl std::fmt::Display for CommitError {
+impl std::fmt::Display for TourError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Self::NotADescendantOfCurrentDir(path) => {
-                write!(f, "File {:?} is not a descendant of the working directory.", path)
-            }
-            Self::InsideTourDir(path) => {
-                write!(f, "File {:?} is inside a .tour directory, which is not allowed.", path)
+            Self::NoTour => {
+                write!(f, "No tour found in this directory. Run `tour init` first.")
             }
+            Self::TourAlreadyExists => write!(f, "A tour already exists in this directory."),
+            Self::TourEnded => write!(f, "Tour has already been ended."),
             Self::NothingToCommit => {
                 write!(f, "Nothing to commit. Use `tour add <files>` to stage files first.")
             }
-            Self::Io(e) => write!(f, "IO error: {}", e),
+            Self::NoSteps => {
+                write!(f, "Cannot end a tour with no steps. Use `tour commit` to add steps first.")
+            }
+            Self::NotADescendant(p) => {
+                write!(f, "File {:?} is not a descendant of the working directory.", p)
+            }
+            Self::InsideTourDir(p) => {
+                write!(f, "File {:?} is inside a .tour directory, which is not allowed.", p)
+            }
+            Self::FileNotFound(p) => write!(f, "File not found: {}", p.display()),
+            Self::StepOutOfRange { step, total } => {
+                write!(f, "Step {} is out of range (1-{}).", step, total)
+            }
+            Self::CorruptedTour(msg) => write!(f, "Tour data is corrupted: {}", msg),
+            Self::Io(e) => write!(f, "{}", e),
         }
     }
 }
 
-impl std::error::Error for CommitError {}
+impl std::error::Error for TourError {}
 
-impl From<io::Error> for CommitError {
+impl From<io::Error> for TourError {
     fn from(e: io::Error) -> Self {
         Self::Io(e)
     }