feat: add 40 slash commands — command surface 67/141

Port 40 missing user-facing slash commands from upstream parity audit:

Session: /doctor, /login, /logout, /usage, /stats, /rename, /privacy-settings
Workspace: /branch, /add-dir, /files, /hooks, /release-notes
Discovery: /context, /tasks, /doctor, /ide, /desktop
Analysis: /review, /security-review, /advisor, /insights
Appearance: /theme, /vim, /voice, /color, /effort, /fast, /brief,
  /output-style, /keybindings, /stickers
Communication: /copy, /share, /feedback, /summary, /tag, /thinkback,
  /plan, /exit, /upgrade, /rewind

All commands have full SlashCommandSpec, enum variant, parse arm,
and stub handler. Category system expanded with two new categories.
Tests updated for new counts (67 specs, 39 resume-supported).
fmt/clippy/tests all green.

rust/crates/rusty-claude-cli/tests/cli_flags_and_config_defaults.rs

@@ -80,7 +80,7 @@ fn slash_command_names_match_known_commands_and_suggest_nearby_unknown_ones() {
         .expect("claw should launch");
     let unknown_output = Command::new(env!("CARGO_BIN_EXE_claw"))
         .current_dir(&temp_dir)
-        .arg("/stats")
+        .arg("/zstats")
         .output()
         .expect("claw should launch");
 
@@ -97,7 +97,7 @@ fn slash_command_names_match_known_commands_and_suggest_nearby_unknown_ones() {
         String::from_utf8_lossy(&unknown_output.stderr)
     );
     let stderr = String::from_utf8(unknown_output.stderr).expect("stderr should be utf8");
-    assert!(stderr.contains("unknown slash command outside the REPL: /stats"));
+    assert!(stderr.contains("unknown slash command outside the REPL: /zstats"));
     assert!(stderr.contains("Did you mean"));
     assert!(stderr.contains("/status"));