feat: scaffold Phase B + C (events, telemetry, plugins, Solid.js)

Phase B Step 6 — Solid.js incremental migration
  - vite-plugin-solid + solid-js + @solidjs/testing-library in package.json
  - vite.config.ts compiles src/components/solid/** as Solid TSX
  - tsconfig.json gains jsx: preserve / jsxImportSource: solid-js
  - lib/solidAdapter.ts wraps existing custom Stores as Solid signals
  - lib/solidMount.ts adapts Solid render to {mount,destroy} contract
  - components/solid/Badge.tsx (proof-of-concept leaf)
  - components/solid/ChannelListItem.tsx (store-subscribed leaf)
  - components/solid/Badge.test.tsx pipeline smoke test
  - components/solid/README.md documents the migration recipe

Phase B Step 7 — Event persistence layer
  - SQLite + Postgres migrations for the events table
  - sqlc query files for both engines
  - EventStore interface + SQLite raw-SQL impl + MemStore impl + pg stubs
  - ws.EventPersister: async batched writer (queue / flush / drain / drop)
  - ws.StartEventPruner: background retention pruner
  - hub persists every replay-buffer push and exposes reconnect-tier counters
  - serve.handleReconnect: tiered replay (buffer -> DB -> full re-sync)
  - EventPersistenceConfig + main.go wiring
  - event_persister_test.go covers batching / drops / drain

Phase B Step 8 — OpenTelemetry skeleton
  - Server/telemetry package with public Provider/Tracer/Meter/Counter API
  - telemetry_default.go (no-op build) + telemetry_otel.go (build tag otel)
  - telemetry/metrics.go declares the AppMetrics bundle
  - HTTPMiddleware mounted in Chi router (pass-through in default build)
  - PrometheusHandler optionally mounted at /metrics
  - Spans on MessageService.SendMessage, PermissionService.HasChannelPerm,
    ChannelService.ListVisibleChannels
  - Reconnect-tier counter wired into the global meter
  - TelemetryConfig defaults

Phase C Step 9 — Wazero plugin runtime skeleton
  - Server/plugin package: manifest parser, loader, registry, host APIs
    (commands, storage, events, http, ui), errors
  - sandbox_default.go (no-op) + sandbox_wazero.go (build tag wazero)
  - SQLite + Postgres migrations for plugins + plugin_kv tables
  - PluginStore interface + impls + pg stubs
  - plugin/examples/hello manifest + README
  - plugin_test.go covers manifest, loader, capability gating
  - api/plugins_handler.go admin REST surface, mounted under admin group
  - PluginsConfig + main.go wiring (disabled by default)
  - Client: lib/pluginBridge.ts iframe + postMessage host
  - Client: components/solid/PluginContainer.tsx Solid host component

Verification
  - Default build (no -tags) is intended to compile cleanly with no new
    third-party dependencies. The sandbox lacked Go 1.25.0 so go build
    could not run; PHASE_BC_LOCAL_TODO.md enumerates the local follow-up
    work (npm install, go mod tidy, sqlc-generate, real otel/wazero
    wiring, remaining service spans, full Solid migration).

Server/db/persisted_event.go

@@ -0,0 +1,27 @@
+package db
+
+import "time"
+
+// PersistedEvent is a single broadcast event written to the events table for
+// cold-replay during reconnection. The event payload is the same wire-format
+// JSON the WebSocket clients receive at broadcast time, including the seq
+// field injected by the hub.
+//
+// Phase B Step 7 (event persistence layer).
+type PersistedEvent struct {
+	Seq       int64
+	EventType string
+	ChannelID int64
+	Payload   []byte
+	CreatedAt time.Time
+}
+
+// PluginRow represents a row in the plugins table (Phase C Step 9).
+type PluginRow struct {
+	ID           int64
+	Name         string
+	Version      string
+	Enabled      bool
+	ManifestJSON string
+	InstalledAt  time.Time
+}

Server/db/queries/postgres/events.sql

@@ -0,0 +1,14 @@
+-- name: PersistEvent :one
+INSERT INTO events (event_type, channel_id, payload)
+VALUES ($1, $2, $3)
+RETURNING seq;
+
+-- name: GetEventsSince :many
+SELECT seq, event_type, channel_id, payload, created_at
+FROM events
+WHERE seq > $1
+ORDER BY seq ASC
+LIMIT $2;
+
+-- name: PruneEventsOlderThan :execrows
+DELETE FROM events WHERE created_at < $1;

Server/db/queries/postgres/plugins.sql

@@ -0,0 +1,36 @@
+-- name: InstallPlugin :one
+INSERT INTO plugins (name, version, manifest_json)
+VALUES ($1, $2, $3)
+ON CONFLICT (name) DO UPDATE
+   SET version = excluded.version,
+       manifest_json = excluded.manifest_json
+RETURNING id;
+
+-- name: EnablePlugin :exec
+UPDATE plugins SET enabled = TRUE WHERE id = $1;
+
+-- name: DisablePlugin :exec
+UPDATE plugins SET enabled = FALSE WHERE id = $1;
+
+-- name: UninstallPlugin :exec
+DELETE FROM plugins WHERE id = $1;
+
+-- name: GetPlugin :one
+SELECT id, name, version, enabled, manifest_json, installed_at FROM plugins WHERE id = $1;
+
+-- name: GetPluginByName :one
+SELECT id, name, version, enabled, manifest_json, installed_at FROM plugins WHERE name = $1;
+
+-- name: ListPlugins :many
+SELECT id, name, version, enabled, manifest_json, installed_at FROM plugins ORDER BY name;
+
+-- name: PluginKVGet :one
+SELECT value FROM plugin_kv WHERE plugin_id = $1 AND key = $2;
+
+-- name: PluginKVSet :exec
+INSERT INTO plugin_kv (plugin_id, key, value)
+VALUES ($1, $2, $3)
+ON CONFLICT (plugin_id, key) DO UPDATE SET value = excluded.value;
+
+-- name: PluginKVDelete :exec
+DELETE FROM plugin_kv WHERE plugin_id = $1 AND key = $2;

Server/db/queries/sqlite/events.sql

@@ -0,0 +1,12 @@
+-- name: PersistEvent :execresult
+INSERT INTO events (event_type, channel_id, payload) VALUES (?, ?, ?);
+
+-- name: GetEventsSince :many
+SELECT seq, event_type, channel_id, payload, created_at
+FROM events
+WHERE seq > ?
+ORDER BY seq ASC
+LIMIT ?;
+
+-- name: PruneEventsOlderThan :execrows
+DELETE FROM events WHERE created_at < ?;

Server/db/queries/sqlite/plugins.sql

@@ -0,0 +1,31 @@
+-- name: InstallPlugin :execresult
+INSERT INTO plugins (name, version, manifest_json) VALUES (?, ?, ?)
+ON CONFLICT(name) DO UPDATE SET version = excluded.version, manifest_json = excluded.manifest_json;
+
+-- name: EnablePlugin :exec
+UPDATE plugins SET enabled = 1 WHERE id = ?;
+
+-- name: DisablePlugin :exec
+UPDATE plugins SET enabled = 0 WHERE id = ?;
+
+-- name: UninstallPlugin :exec
+DELETE FROM plugins WHERE id = ?;
+
+-- name: GetPlugin :one
+SELECT id, name, version, enabled, manifest_json, installed_at FROM plugins WHERE id = ?;
+
+-- name: GetPluginByName :one
+SELECT id, name, version, enabled, manifest_json, installed_at FROM plugins WHERE name = ?;
+
+-- name: ListPlugins :many
+SELECT id, name, version, enabled, manifest_json, installed_at FROM plugins ORDER BY name;
+
+-- name: PluginKVGet :one
+SELECT value FROM plugin_kv WHERE plugin_id = ? AND key = ?;
+
+-- name: PluginKVSet :exec
+INSERT INTO plugin_kv (plugin_id, key, value) VALUES (?, ?, ?)
+ON CONFLICT(plugin_id, key) DO UPDATE SET value = excluded.value;
+
+-- name: PluginKVDelete :exec
+DELETE FROM plugin_kv WHERE plugin_id = ? AND key = ?;