feat(aircoding): AirCoding V2 baseline — deterministic multi-agent architecture

Forked from OpenCode v1.17.4 with multi-agent system:
- 5 agents: aircoding, scheduler, worker, architect, reviewer
- Deterministic DAG scheduling engine (coordinator_tick)
- Tool whitelists as hard enforcement
- AirCoding validation plugin
- System prompt injection for routing
- V1 requirements: C4 docs, ADR, AGENTS.md, debug-log.md
- Design documents in docs/

packages/opencode/specs/v2/notifications.md

@@ -0,0 +1,13 @@
+# TUI Notifications Default
+
+Problem:
+
+- v1 defaults `attention.enabled` to `false`
+- users can opt in with `attention.enabled = true`
+- v2 should make core TUI notifications a default behavior
+
+## v2 Target
+
+Flip `attention.enabled` to `true` by default in v2.
+
+Keep `attention.enabled = false` as the explicit opt-out.