fix(brain): Postgres portability for brain connection + migrations

Three related fixes so the brain DB works on Postgres, not just MariaDB:

1. config.php — brain charset/collation was hardcoded to utf8mb4 which
   Postgres rejects as client_encoding. Now driver-aware: utf8 for
   pgsql, utf8mb4 otherwise. Override via BRAIN_DB_CHARSET env var.

2. Migration 000008 (create_brain_memories) — self-referential FK on
   supersedes_id was declared inside Schema::create{}, causing Postgres
   to evaluate it before the PK index existed ('no unique constraint
   matching given keys'). Split into Schema::create + separate
   Schema::table to guarantee PK is in place when FK is added.

3. Migration 000009 (drop workspace FK) — try/catch inside the Blueprint
   closure couldn't catch deferred SQL failures. Replaced with a
   constraint-exists pre-query against information_schema, supporting
   both pgsql and mariadb/mysql drivers. Fresh installs no longer fail
   trying to drop a constraint that was never created.

Co-Authored-By: Virgil <virgil@lethean.io>

php/Migrations/0001_01_01_000008_create_brain_memories_table.php

@@ -43,7 +43,15 @@ return new class extends Migration
                 $table->index('agent_id');
                 $table->index(['workspace_id', 'type']);
                 $table->index(['workspace_id', 'project']);
+            });
 
+            // Self-referential FK added AFTER create so Postgres sees the
+            // primary key on `id` when evaluating the constraint. Adding it
+            // inside the create{} block ordered the FK before the PK index
+            // on some Postgres versions, breaking with:
+            //   SQLSTATE[42830]: there is no unique constraint matching
+            //   given keys for referenced table "brain_memories"
+            $schema->table('brain_memories', function (Blueprint $table) {
                 $table->foreign('supersedes_id')
                     ->references('id')
                     ->on('brain_memories')

php/Migrations/0001_01_01_000009_drop_brain_memories_workspace_fk.php

@@ -25,13 +25,34 @@ return new class extends Migration
             return;
         }
 
-        $schema->table('brain_memories', function (Blueprint $table) {
-            try {
+        // Laravel Blueprint defers statement execution until the closure
+        // returns, so a try/catch INSIDE the closure doesn't catch the
+        // deferred SQL's failure. Instead, check the constraint exists
+        // before issuing the drop, across both pgsql + mariadb backends.
+        $conn = $schema->getConnection();
+        $driver = $conn->getDriverName();
+        $constraint = 'brain_memories_workspace_id_foreign';
+
+        $exists = match ($driver) {
+            'pgsql' => (bool) $conn->selectOne(
+                "SELECT 1 FROM information_schema.table_constraints
+                 WHERE table_name = 'brain_memories' AND constraint_name = ?",
+                [$constraint],
+            ),
+            'mariadb', 'mysql' => (bool) $conn->selectOne(
+                "SELECT 1 FROM information_schema.table_constraints
+                 WHERE table_schema = DATABASE() AND table_name = 'brain_memories'
+                       AND constraint_name = ?",
+                [$constraint],
+            ),
+            default => false,   // unknown driver — don't attempt the drop
+        };
+
+        if ($exists) {
+            $schema->table('brain_memories', function (Blueprint $table) {
                 $table->dropForeign(['workspace_id']);
-            } catch (\Throwable) {
-                // FK doesn't exist — fresh install, nothing to drop.
-            }
-        });
+            });
+        }
     }
 
     public function down(): void

php/config.php

@@ -95,8 +95,11 @@ return [
             'database' => env('BRAIN_DB_DATABASE', env('DB_DATABASE', 'forge')),
             'username' => env('BRAIN_DB_USERNAME', env('DB_USERNAME', 'forge')),
             'password' => env('BRAIN_DB_PASSWORD', env('DB_PASSWORD', '')),
-            'charset' => 'utf8mb4',
-            'collation' => 'utf8mb4_unicode_ci',
+            // charset defaults: utf8 for pgsql (Postgres rejects 'utf8mb4'),
+            // utf8mb4 for everything else (MariaDB/MySQL). Override with
+            // BRAIN_DB_CHARSET if your instance needs something specific.
+            'charset' => env('BRAIN_DB_CHARSET', env('BRAIN_DB_DRIVER', env('DB_CONNECTION', 'mariadb')) === 'pgsql' ? 'utf8' : 'utf8mb4'),
+            'collation' => env('BRAIN_DB_COLLATION', 'utf8mb4_unicode_ci'),
             'prefix' => '',
         ],
     ],