feat(who): expand expert + overlap queries with mr_file_changes and mr_reviewers

Chain: bd-jec (config flag) -> bd-2yo (fetch MR diffs) -> bd-3qn6 (rewrite who queries)

- Add fetch_mr_file_changes config option and --no-file-changes CLI flag
- Add GitLab MR diffs API fetch pipeline with watermark-based sync
- Create migration 020 for diffs_synced_for_updated_at watermark column
- Rewrite query_expert() and query_overlap() to use 4-signal UNION ALL:
  DiffNote reviewers, DiffNote MR authors, file-change authors, file-change reviewers
- Deduplicate across signal types via COUNT(DISTINCT CASE WHEN ... THEN mr_id END)
- Add insert_file_change test helper, 8 new who tests, all 397 tests pass
- Also includes: list performance migration 019, autocorrect module, README updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/mod.rs

@@ -1,3 +1,4 @@
+pub mod autocorrect;
 pub mod commands;
 pub mod progress;
 pub mod robot;
@@ -81,13 +82,18 @@ impl Cli {
 
     /// Detect robot mode from environment before parsing succeeds.
     /// Used for structured error output when clap parsing fails.
+    /// Also catches common agent typos like `-robot` and `--Robot`.
     pub fn detect_robot_mode_from_env() -> bool {
         let args: Vec<String> = std::env::args().collect();
-        args.iter()
-            .any(|a| a == "--robot" || a == "-J" || a == "--json")
-            || std::env::var("LORE_ROBOT")
-                .ok()
-                .is_some_and(|v| !v.is_empty() && v != "0" && v != "false")
+        args.iter().any(|a| {
+            a == "-J"
+                || a.eq_ignore_ascii_case("--robot")
+                || a.eq_ignore_ascii_case("-robot")
+                || a.eq_ignore_ascii_case("--json")
+                || a.eq_ignore_ascii_case("-json")
+        }) || std::env::var("LORE_ROBOT")
+            .ok()
+            .is_some_and(|v| !v.is_empty() && v != "0" && v != "false")
             || !std::io::stdout().is_terminal()
     }
 }
@@ -608,6 +614,10 @@ pub struct SyncArgs {
     #[arg(long = "no-events")]
     pub no_events: bool,
 
+    /// Skip MR file change fetching (overrides config)
+    #[arg(long = "no-file-changes")]
+    pub no_file_changes: bool,
+
     /// Preview what would be synced without making changes
     #[arg(long, overrides_with = "no_dry_run")]
     pub dry_run: bool,