feat(reviewer): add Tier 1 reviewer agent role with auto-channel notifications

Reviewer workflow in agent-prompts.ts (8-step process), Rust auto-post
to #review-queue on task->review transition, reviewQueueDepth in
attention scoring (10pts/task cap 50), Tasks tab for reviewer in
ProjectBox with 10s queue polling. 7 vitest + 4 cargo tests.

v2/src-tauri/src/lib.rs

@@ -147,6 +147,7 @@ pub fn run() {
             commands::bttask::bttask_add_comment,
             commands::bttask::bttask_create,
             commands::bttask::bttask_delete,
+            commands::bttask::bttask_review_queue_count,
             // Misc
             commands::misc::cli_get_group,
             commands::misc::open_url,