Converge the release REPL hardening onto the redesigned CLI

The release branch keeps feat/uiux-redesign as the primary UX surface and only reapplies the hardening changes that still add value there. REPL turns now preserve raw user input, REPL-only unknown slash command guidance can suggest exit shortcuts alongside shared commands, slash completion includes /exit and /quit, and the shared help copy keeps the grouped redesign while making resume guidance a little clearer.

The release-facing README and 0.1.0 draft notes already matched the current release-doc wording, so no extra docs delta was needed in this convergence commit.

Constraint: Keep the redesigned startup/help/status surfaces intact for release/0.1.0
Constraint: Do not reintroduce blanket prompt trimming before runtime submission
Rejected: Port the hardening branch's editor-mode/config path wholesale | it diverged from the redesigned custom line editor and would have regressed the release UX
Rejected: Flatten grouped slash help back into per-command blocks | weaker fit for the redesign's operator-style help surface
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep REPL-only suggestions and completion candidates aligned when adding or removing /vim, /exit, or /quit behavior
Tested: cargo check
Tested: cargo test
Not-tested: Live provider-backed REPL turns and interactive terminal manual QA

rust/crates/commands/src/lib.rs

@@ -488,7 +488,7 @@ pub fn render_slash_command_help() -> String {
     let mut lines = vec![
         "Slash commands".to_string(),
         "  Tab completes commands inside the REPL.".to_string(),
-        "  [resume] works with --resume SESSION.json.".to_string(),
+        "  [resume] = also available via claw --resume SESSION.json".to_string(),
     ];
 
     for category in [
@@ -2108,7 +2108,7 @@ mod tests {
     #[test]
     fn renders_help_from_shared_specs() {
         let help = render_slash_command_help();
-        assert!(help.contains("works with --resume SESSION.json"));
+        assert!(help.contains("available via claw --resume SESSION.json"));
         assert!(help.contains("Core flow"));
         assert!(help.contains("Workspace & memory"));
         assert!(help.contains("Sessions & output"));