fix: Plugin migration runner + unified_search + marketplace migrations

Fixes 3 issues found by API integration tests:
1. migration_runner.py: Add GLOBAL TABLE exemption for tables without tenant_id
   - New _extract_global_table_names() method parses -- GLOBAL TABLE: comments
   - marketplace_listings is intentionally global (no tenant_id)
2. unified_search/migrations/0002_embeddings.sql: Remove companies table (does not exist),
   add DO $$ BEGIN END $$ blocks to check table existence before ALTER
3. marketplace/migrations/0001_initial.sql: Add -- GLOBAL TABLE: marketplace_listings comment

app/plugins/builtins/unified_search/migrations/0002_embeddings.sql

@@ -1,27 +1,45 @@
 -- Unified Search: Embedding columns and HNSW indexes
+-- Note: These columns are also added by Alembic migration 0104.
+-- This migration is idempotent (IF NOT EXISTS) and skips non-existent tables.
 
 -- Ensure pgvector extension is installed
 CREATE EXTENSION IF NOT EXISTS vector;
 
 -- ─── Mails ───
-ALTER TABLE mails ADD COLUMN IF NOT EXISTS embedding vector(768);
-CREATE INDEX IF NOT EXISTS ix_mails_embedding ON mails USING hnsw(embedding vector_cosine_ops);
+DO $$ BEGIN
+  IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'mails') THEN
+    ALTER TABLE mails ADD COLUMN IF NOT EXISTS embedding vector(768);
+    CREATE INDEX IF NOT EXISTS ix_mails_embedding ON mails USING hnsw(embedding vector_cosine_ops);
+  END IF;
+END $$;
 
 -- ─── Contacts ───
-ALTER TABLE contacts ADD COLUMN IF NOT EXISTS embedding vector(768);
-CREATE INDEX IF NOT EXISTS ix_contacts_embedding ON contacts USING hnsw(embedding vector_cosine_ops);
+DO $$ BEGIN
+  IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'contacts') THEN
+    ALTER TABLE contacts ADD COLUMN IF NOT EXISTS embedding vector(768);
+    CREATE INDEX IF NOT EXISTS ix_contacts_embedding ON contacts USING hnsw(embedding vector_cosine_ops);
+  END IF;
+END $$;
 
--- ─── Companies ───
-ALTER TABLE companies ADD COLUMN IF NOT EXISTS embedding vector(768);
-CREATE INDEX IF NOT EXISTS ix_companies_embedding ON companies USING hnsw(embedding vector_cosine_ops);
-
--- ─── Files (content_text already added in 0001) ───
-ALTER TABLE files ADD COLUMN IF NOT EXISTS embedding vector(768);
-CREATE INDEX IF NOT EXISTS ix_files_embedding ON files USING hnsw(embedding vector_cosine_ops);
+-- ─── Files ───
+DO $$ BEGIN
+  IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'files') THEN
+    ALTER TABLE files ADD COLUMN IF NOT EXISTS embedding vector(768);
+    CREATE INDEX IF NOT EXISTS ix_files_embedding ON files USING hnsw(embedding vector_cosine_ops);
+  END IF;
+END $$;
 
 -- ─── Calendar Entries ───
-ALTER TABLE calendar_entries ADD COLUMN IF NOT EXISTS embedding vector(768);
-CREATE INDEX IF NOT EXISTS ix_cal_embedding ON calendar_entries USING hnsw(embedding vector_cosine_ops);
+DO $$ BEGIN
+  IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'calendar_entries') THEN
+    ALTER TABLE calendar_entries ADD COLUMN IF NOT EXISTS embedding vector(768);
+    CREATE INDEX IF NOT EXISTS ix_cal_embedding ON calendar_entries USING hnsw(embedding vector_cosine_ops);
+  END IF;
+END $$;
 
 -- ─── Tags (shorter dimension for short text) ───
-ALTER TABLE tags ADD COLUMN IF NOT EXISTS embedding vector(384);
+DO $$ BEGIN
+  IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'tags') THEN
+    ALTER TABLE tags ADD COLUMN IF NOT EXISTS embedding vector(384);
+  END IF;
+END $$;