Fixes for M-02 to M-14, G-01 to G-14, K-02 to K-04, X-04 to X-14, not yet reviewed

Committed before review so Windows and WSL builds can start.
Each fix was tested and mutation-checked here; the codex review
of each item is still to come, so tasks/BUGS.md stays unticked.

M-02 is mid-review: round 1 findings are fixed (apps/ely-mark/src/tally.rs).
K-01 stays deferred. The ElyMark window test mark-outside.sh failed
once at its crash-recovery step in the last run; not yet looked into.

apps/ely-tree/src/git.rs

@@ -74,6 +74,13 @@ impl Git {
         checked(args, output)
     }
 
+    /// HEAD names a commit; a new repository has none yet.
+    pub fn born(&self, dir: &Path) -> io::Result<bool> {
+        Ok(!self
+            .run_or_one(dir, &["rev-parse", "--verify", "-q", "HEAD"])?
+            .is_empty())
+    }
+
     /// Exit 1 is an answer: files differ, key unset.
     pub fn run_or_one(&self, dir: &Path, args: &[&str]) -> io::Result<Vec<u8>> {
         let output = self.command(dir, args).output()?;