refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

packages/tfcode/migration/20260228203230_blue_harpoon/migration.sql

@@ -0,0 +1,17 @@
+CREATE TABLE `account` (
+	`id` text PRIMARY KEY,
+	`email` text NOT NULL,
+	`url` text NOT NULL,
+	`access_token` text NOT NULL,
+	`refresh_token` text NOT NULL,
+	`token_expiry` integer,
+	`selected_org_id` text,
+	`time_created` integer NOT NULL,
+	`time_updated` integer NOT NULL
+);
+--> statement-breakpoint
+CREATE TABLE `account_state` (
+	`id` integer PRIMARY KEY NOT NULL,
+	`active_account_id` text,
+	FOREIGN KEY (`active_account_id`) REFERENCES `account`(`id`) ON UPDATE no action ON DELETE set null
+);