feat: initial scaffold of kanban_cpp v2 (issue 0130)

Frontend C++ ImGui (main.cpp + 4 paneles) + backend Go (HTTP + SQLite + fsnotify + SSE).
Reusa parse/scan/watch funcs del registry (issue 0130a).

backend/migrations/001_init.sql

@@ -0,0 +1,34 @@
+CREATE TABLE IF NOT EXISTS issues (
+    id           TEXT PRIMARY KEY,
+    title        TEXT NOT NULL,
+    status       TEXT NOT NULL,
+    type         TEXT,
+    scope        TEXT,
+    priority     TEXT,
+    domain_json  TEXT NOT NULL DEFAULT '[]',
+    tags_json    TEXT NOT NULL DEFAULT '[]',
+    depends_json TEXT NOT NULL DEFAULT '[]',
+    blocks_json  TEXT NOT NULL DEFAULT '[]',
+    related_json TEXT NOT NULL DEFAULT '[]',
+    flow_id      TEXT,
+    body         TEXT NOT NULL DEFAULT '',
+    file_path    TEXT NOT NULL,
+    mtime_ns     INTEGER NOT NULL,
+    created_at   TEXT,
+    updated_at   TEXT,
+    completed    INTEGER NOT NULL DEFAULT 0
+);
+CREATE INDEX IF NOT EXISTS idx_issues_status   ON issues(status);
+CREATE INDEX IF NOT EXISTS idx_issues_priority ON issues(priority);
+CREATE INDEX IF NOT EXISTS idx_issues_scope    ON issues(scope);
+
+CREATE TABLE IF NOT EXISTS flows (
+    id        TEXT PRIMARY KEY,
+    title     TEXT NOT NULL,
+    status    TEXT,
+    kind      TEXT,
+    tags_json TEXT NOT NULL DEFAULT '[]',
+    body      TEXT NOT NULL DEFAULT '',
+    file_path TEXT NOT NULL,
+    mtime_ns  INTEGER NOT NULL
+);