refactor(store): migration files + embed.FS

- migrations/001_init.sql + 002_target_extras.sql extraidos de schema inline
- store.go: applyMigrations() con embed.FS, splitSQLStatements, isIdempotentError
- aplica regla db_migrations.md (fn_registry/.claude/rules/)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migrations/001_init.sql

@@ -0,0 +1,26 @@
+-- deploy_server initial schema. Tracks deploy targets (per app+host) and execution history.
+
+CREATE TABLE IF NOT EXISTS deploy_targets (
+    app           TEXT NOT NULL,
+    host          TEXT NOT NULL,
+    remote_dir    TEXT NOT NULL DEFAULT '',
+    binary_name   TEXT NOT NULL DEFAULT '',
+    build_cmd     TEXT NOT NULL DEFAULT '',
+    service_user  TEXT NOT NULL DEFAULT '',
+    port          INTEGER NOT NULL DEFAULT 0,
+    health_path   TEXT NOT NULL DEFAULT '',
+    env           TEXT NOT NULL DEFAULT '{}',
+    created_at    TEXT NOT NULL,
+    PRIMARY KEY (app, host)
+);
+
+CREATE TABLE IF NOT EXISTS deploy_logs (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    app         TEXT NOT NULL,
+    host        TEXT NOT NULL,
+    status      TEXT NOT NULL,
+    trigger     TEXT NOT NULL DEFAULT 'manual',
+    error       TEXT NOT NULL DEFAULT '',
+    duration_ms INTEGER NOT NULL DEFAULT 0,
+    started_at  TEXT NOT NULL
+);