feat: Extract search into pluggable provider system (outline#11448)

* feat: Extract search into pluggable provider system

Refactors the monolithic SearchHelper into a pluggable search provider
architecture, enabling alternative search backends (Elasticsearch,
Turbopuffer, etc.) while preserving PostgreSQL full-text search as the
default. The SEARCH_PROVIDER env var selects the active provider.

- Add BaseSearchProvider abstract class and SearchProviderManager
- Add Hook.SearchProvider to the plugin system
- Move PostgreSQL search logic into plugins/postgres-search/
- Add SearchIndexProcessor for event-driven index sync
- Update all callers to use the provider manager directly
- Keep SearchHelper as a deprecated thin wrapper for backwards compat

Closes outline#11347

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: Remove deprecated SearchHelper wrapper

All callers now use SearchProviderManager directly, so the thin
delegation wrapper is no longer needed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: Rename postgres-search plugin to search-postgres

Renames the plugin folder and id so that future search provider plugins
(e.g. search-elasticsearch, search-turbopuffer) will be colocated
alphabetically.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: Remove special-case plugin import from SearchProviderManager

Make PluginManager.loadPlugins resilient to individual plugin load
failures so SearchProviderManager can use the standard getHooks path
without needing to directly import the search-postgres plugin.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: Add missing search provider tests for full coverage parity

Adds all tests that existed in the old SearchHelper.test.ts but were missing
from PostgresSearchProvider.test.ts, including searchTitlesForUser status
filters, collection filtering, group memberships, and sorting tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feedback

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: tommoor

app/stores/UnfurlsStore.ts

@@ -24,7 +24,11 @@ class UnfurlsStore extends Store<Unfurl<any>> {
   }): Promise<Unfurl<UnfurlType> | undefined> => {
     try {
       const protocol = new URL(url).protocol;
-      if (protocol !== "http:" && protocol !== "https:" && protocol !== "mention:") {
+      if (
+        protocol !== "http:" &&
+        protocol !== "https:" &&
+        protocol !== "mention:"
+      ) {
         return;
       }
     } catch (_err) {

plugins/search-postgres/plugin.json

@@ -0,0 +1,6 @@
+{
+  "id": "search-postgres",
+  "name": "PostgreSQL Search",
+  "priority": 0,
+  "description": "Full-text search powered by PostgreSQL tsvector."
+}