[BUG] Default command loader scans wrong dirs (command/Cortex vs commands/cortex); imported global commands never load #416

Summary

CommandLoader::new() / default() and sync::default_search_dirs() default to command directories that don't match the canonical ones used everywhere else in the crate, so commands imported/written to the standard location are never found by the default loader on case-sensitive filesystems.

Location

src/cortex-commands/src/loader.rs:50 and :54 (duplicated at :248 and :252), at commit 7954d021 (current main).

The loader uses:

• .cortex/command (project-local) — singular command
• config_dir.join("Cortex").join("command") — capital-C Cortex, singular command

But the canonical dirs everywhere else are plural / lowercase:

• .cortex/commands and cortex/commands — manager.rs:110,118,166,170; import.rs:344,348; builtin/commands_cmd.rs.

The loader's own doc comment (loader.rs:44-45) even says lowercase ~/.config/cortex/command/, contradicting the code's "Cortex".

Reproduction

1. Import/place a global command at ~/.config/cortex/commands/foo.md (where CommandManager::import_from / default_command_target write).
2. Call CommandRegistry::load_default() (registry.rs:31-35, uses CommandLoader::new()) or sync::load_all() (builtin/commands_cmd.rs:66).

Expected: foo is loaded.
Actual: not loaded — the loader scans .cortex/command / Cortex/command instead.

Suggested fix

Change both default-dir sites (and the :248/:252 duplicate) to .cortex/commands and config_dir.join("cortex").join("commands"), matching the rest of the crate.