feat: implement lore brief command (bd-1n5q)

Composable capstone: replaces 5+ separate lore calls with a single
situational awareness command. Three modes:
- Topic: lore brief 'authentication'
- Path: lore brief --path src/auth/
- Person: lore brief --person username

Seven sections: open_issues, active_mrs, experts, recent_activity,
unresolved_threads, related (semantic), warnings.

Each section degrades gracefully if data is unavailable.
7 unit tests, robot-docs, autocorrect registry.

src/cli/commands/mod.rs

@@ -1,4 +1,5 @@
 pub mod auth_test;
+pub mod brief;
 pub mod count;
 pub mod doctor;
 pub mod drift;
@@ -22,6 +23,7 @@ pub mod tui;
 pub mod who;
 
 pub use auth_test::run_auth_test;
+pub use brief::{BriefArgs, BriefResponse, print_brief_human, print_brief_json, run_brief};
 pub use count::{
     print_count, print_count_json, print_event_count, print_event_count_json,
     print_reference_count, print_reference_count_json, run_count, run_count_events,