feat(broker+cli): topics — conversation scope within a mesh (v0.2.0)

Adds the third axis of mesh organization: mesh = trust boundary,
group = identity tag, topic = conversation scope. Topic-tagged
messages filter delivery by topic_member rows and persist to a
topic_message history table for back-scroll on reconnect.

Schema (additive):
- mesh.topic, mesh.topic_member, mesh.topic_message tables
- topic_visibility (public|private|dm) and topic_member_role
  (lead|member|observer) enums
- migration 0022_topics.sql, hand-written following project convention
  (drizzle journal has been drifting since 0011)

Broker:
- 10 helpers (createTopic, listTopics, findTopicByName, joinTopic,
  leaveTopic, topicMembers, getMemberTopicIds, appendTopicMessage,
  topicHistory, markTopicRead)
- drainForMember matches "#<topicId>" target_specs via member's
  topic memberships
- 7 WS handlers (topic_create/list/join/leave/members/history/mark_read)
  + resolveTopicId helper accepting id-or-name
- handleSend auto-persists topic-tagged messages to history

CLI:
- claudemesh topic create/list/join/leave/members/history/read
- claudemesh send "#deploys" "..." resolves topic name to id
- bundled skill teaches Claude the DM/group/topic decision matrix
- policy-classify recognizes topic create/join/leave as writes

Spec: .artifacts/specs/2026-05-02-v0.2.0-scope.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/db/migrations/0022_topics.sql

@@ -0,0 +1,66 @@
+-- Topics — conversational primitive within a mesh (v0.2.0).
+--
+-- Spec: .artifacts/specs/2026-05-02-v0.2.0-scope.md
+--
+-- Mesh = trust boundary. Group = identity tag. Topic = conversation scope.
+-- Three orthogonal axes; topics complement (don't replace) groups.
+--
+-- Three new tables in the `mesh` pg-schema:
+--   * mesh.topic            — named topic per mesh (unique on mesh_id, name)
+--   * mesh.topic_member     — per-member subscriptions, with last_read_at
+--   * mesh.topic_message    — persistent encrypted history (used for human-
+--                             touched topics; agent-only topics may opt out)
+--
+-- Two new pg enums:
+--   * mesh.topic_visibility   = public | private | dm
+--   * mesh.topic_member_role  = lead | member | observer
+--
+-- Additive — no breaking changes to existing tables. Safe to deploy before
+-- CLI/broker code knows about topics; the routing layer falls back to the
+-- existing peer/group/* targeting until topic-tagged messages arrive.
+
+CREATE TYPE "mesh"."topic_visibility" AS ENUM ('public', 'private', 'dm');
+CREATE TYPE "mesh"."topic_member_role" AS ENUM ('lead', 'member', 'observer');
+
+CREATE TABLE IF NOT EXISTS "mesh"."topic" (
+  "id" text PRIMARY KEY NOT NULL,
+  "mesh_id" text NOT NULL REFERENCES "mesh"."mesh"("id") ON DELETE CASCADE ON UPDATE CASCADE,
+  "name" text NOT NULL,
+  "description" text,
+  "visibility" "mesh"."topic_visibility" NOT NULL DEFAULT 'public',
+  "created_by_member_id" text REFERENCES "mesh"."member"("id") ON DELETE SET NULL ON UPDATE CASCADE,
+  "created_at" timestamp DEFAULT now() NOT NULL,
+  "archived_at" timestamp
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS "topic_mesh_name_unique"
+  ON "mesh"."topic" ("mesh_id", "name");
+
+CREATE TABLE IF NOT EXISTS "mesh"."topic_member" (
+  "topic_id" text NOT NULL REFERENCES "mesh"."topic"("id") ON DELETE CASCADE ON UPDATE CASCADE,
+  "member_id" text NOT NULL REFERENCES "mesh"."member"("id") ON DELETE CASCADE ON UPDATE CASCADE,
+  "role" "mesh"."topic_member_role" NOT NULL DEFAULT 'member',
+  "joined_at" timestamp DEFAULT now() NOT NULL,
+  "last_read_at" timestamp
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS "topic_member_unique"
+  ON "mesh"."topic_member" ("topic_id", "member_id");
+
+CREATE INDEX IF NOT EXISTS "topic_member_by_member"
+  ON "mesh"."topic_member" ("member_id");
+
+CREATE TABLE IF NOT EXISTS "mesh"."topic_message" (
+  "id" text PRIMARY KEY NOT NULL,
+  "topic_id" text NOT NULL REFERENCES "mesh"."topic"("id") ON DELETE CASCADE ON UPDATE CASCADE,
+  "sender_member_id" text NOT NULL REFERENCES "mesh"."member"("id") ON DELETE CASCADE ON UPDATE CASCADE,
+  "sender_session_pubkey" text,
+  "nonce" text NOT NULL,
+  "ciphertext" text NOT NULL,
+  "created_at" timestamp DEFAULT now() NOT NULL
+);
+
+-- Composite index for the common access pattern: load topic history
+-- ordered by time. Drives the web chat panel's infinite-scroll fetch.
+CREATE INDEX IF NOT EXISTS "topic_message_by_topic_time"
+  ON "mesh"."topic_message" ("topic_id", "created_at");