feat: DM-First v2 architecture - Tanko live on CT 112

Architecture change: DM-First (v2) replaces @mention-in-stream (v1) as primary
agent interaction channel. See ADR-001-dm-topology and ADR-002-dm-routing.

Key changes:
- New DM-first Zulip adapter (adapter_dm.py) deployed on CT 112
  - Registers empty narrow to receive ALL events
  - Demuxes DMs (type: 'private') vs stream events
  - Replies to DMs back in private thread, stream replies to #agent-hub
  - Uses blocking long-poll (dont_block=False) to eliminate rate limiting
- Rewritten ARCHITECTURE.md, CONTEXT.md, PRD.md for v2 DM-First
- New ADRs: ADR-001 (DM Topology), ADR-002 (DM Routing)
- Archived old ADRs: 001, 002, 005 (topic-topology, mention-routing, mention-detection)
- Updated ADRs: 003 (agent-naming), 004 (per-agent-bots), 006 (all-bots-model)
- Updated PI extension (index.ts) with DM-aware patterns
- Tanko agent confirmed responding in both DM and @all-bots in #agent-hub

docs/adr/ADR-003-agent-naming.md

@@ -1,15 +1,11 @@
-# ADR 3: Agent Naming Convention
+# ADR 3: Agent Naming Convention (Unchanged)
 
-**Date**: 2026-04-28
+**Date**: 2026-04-28 | **Status**: Still active — DM architecture does not affect naming
 
 ### Decision
-Each agent bot has a display name in `{name}-bot` format with no spaces, dashes only: `tanko-bot`, `mumuni-bot`, `koonimo-bot`, `koby-bot`, `kagentz-bot`, `abiba-bot`.
+Each agent bot has a display name in `{name}-bot` format: `tanko-bot`, `mumuni-bot`, etc.
 
-### Context
-Zulip @mentions work best with clean, predictable names. No spaces avoids ambiguity in @mention parsing. The `-bot` suffix makes it clear these are automated agents, not human users.
-
-### Consequences
-- @mention format: `@**tanko-bot**`
+### Consequences (Unchanged)
+- DM address: `@**tanko-bot**` (same as @mention format)
 - Email format: `tanko-bot@chat.sysloggh.net`
-- Users must type @tanko-bot (not @tanko)
-- Consistent naming across all 6 agents
+- Consistent naming across all 6 agents