feat: implement lore who — people intelligence commands (5 modes)

Add `lore who` command with 5 query modes answering collaboration questions
using existing DB data (280K notes, 210K discussions, 33K DiffNotes):

- Expert: who knows about a file/directory (DiffNote path analysis + MR breadth scoring)
- Workload: what is a person working on (assigned issues, authored/reviewing MRs, discussions)
- Active: what discussions need attention (unresolved resolvable, global/project-scoped)
- Overlap: who else is touching these files (dual author+reviewer role tracking)
- Reviews: what review patterns does a person have (prefix-based category extraction)

Includes migration 017 (5 composite indexes), CLI skeleton with clap conflicts_with
validation, robot JSON output with input+resolved_input reproducibility, human terminal
output, and 20 unit tests. All quality gates pass.

Closes: bd-1q8z, bd-34rr, bd-2rk9, bd-2ldg, bd-zqpf, bd-s3rc, bd-m7k1, bd-b51e,
bd-2711, bd-1rdi, bd-3mj2, bd-tfh3, bd-zibc, bd-g0d5

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

migrations/017_who_indexes.sql

@@ -0,0 +1,28 @@
+-- Migration 017: Composite indexes for `who` query paths
+
+-- Expert/Overlap: DiffNote path prefix + timestamp filter.
+CREATE INDEX IF NOT EXISTS idx_notes_diffnote_path_created
+    ON notes(position_new_path, created_at, project_id)
+    WHERE note_type = 'DiffNote' AND is_system = 0;
+
+-- Active/Workload: discussion participation lookups.
+CREATE INDEX IF NOT EXISTS idx_notes_discussion_author
+    ON notes(discussion_id, author_username)
+    WHERE is_system = 0;
+
+-- Active (project-scoped): unresolved discussions by recency, scoped by project.
+CREATE INDEX IF NOT EXISTS idx_discussions_unresolved_recent
+    ON discussions(project_id, last_note_at)
+    WHERE resolvable = 1 AND resolved = 0;
+
+-- Active (global): unresolved discussions by recency (no project scope).
+CREATE INDEX IF NOT EXISTS idx_discussions_unresolved_recent_global
+    ON discussions(last_note_at)
+    WHERE resolvable = 1 AND resolved = 0;
+
+-- Workload: issue assignees by username.
+CREATE INDEX IF NOT EXISTS idx_issue_assignees_username
+    ON issue_assignees(username, issue_id);
+
+INSERT INTO schema_version (version, applied_at, description)
+VALUES (17, strftime('%s', 'now') * 1000, 'Composite indexes for who query paths');