feat: initial scaffold kanban_cpp v0.1.0

C++ ImGui kanban for steering LLM agents. Six panels (Board, Calendar,
Dashboard, Agent runs, Worktrees, DoD inspector) wired to registry
functions http_request, kpi_card, sparkline, agent_runs_timeline,
dod_evidence_panel. Backend Go on :8403 (independent operations.db from
kanban_web).

backend/migrations/001_init.sql

@@ -0,0 +1,51 @@
+CREATE TABLE IF NOT EXISTS columns (
+    id          TEXT PRIMARY KEY,
+    name        TEXT NOT NULL,
+    position    INTEGER NOT NULL DEFAULT 0,
+    location    TEXT NOT NULL DEFAULT 'board' CHECK(location IN ('board','sidebar')),
+    width       INTEGER NOT NULL DEFAULT 300,
+    wip_limit   INTEGER NOT NULL DEFAULT 0,
+    created_at  TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS cards (
+    id          TEXT PRIMARY KEY,
+    requester   TEXT NOT NULL DEFAULT '',
+    title       TEXT NOT NULL,
+    description TEXT NOT NULL DEFAULT '',
+    color       TEXT NOT NULL DEFAULT '',
+    column_id   TEXT NOT NULL REFERENCES columns(id) ON DELETE CASCADE,
+    position    INTEGER NOT NULL DEFAULT 0,
+    locked      INTEGER NOT NULL DEFAULT 0,
+    created_at  TEXT NOT NULL,
+    updated_at  TEXT NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS card_column_history (
+    id         TEXT PRIMARY KEY,
+    card_id    TEXT NOT NULL REFERENCES cards(id) ON DELETE CASCADE,
+    column_id  TEXT NOT NULL,
+    entered_at TEXT NOT NULL,
+    exited_at  TEXT
+);
+
+CREATE TABLE IF NOT EXISTS card_lock_history (
+    id         TEXT PRIMARY KEY,
+    card_id    TEXT NOT NULL REFERENCES cards(id) ON DELETE CASCADE,
+    locked_at  TEXT NOT NULL,
+    unlocked_at TEXT
+);
+
+CREATE TABLE IF NOT EXISTS users (
+    id            TEXT PRIMARY KEY,
+    username      TEXT NOT NULL UNIQUE,
+    password_hash TEXT NOT NULL,
+    display_name  TEXT NOT NULL DEFAULT '',
+    created_at    TEXT NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS idx_cards_column ON cards(column_id);
+CREATE INDEX IF NOT EXISTS idx_cards_position ON cards(column_id, position);
+CREATE INDEX IF NOT EXISTS idx_history_card ON card_column_history(card_id);
+CREATE INDEX IF NOT EXISTS idx_columns_position ON columns(position);
+CREATE INDEX IF NOT EXISTS idx_lock_history_card ON card_lock_history(card_id);