feat(query): add overview() for project-aware session/memory discovery

Resolves current project from cwd, lists all known projects with session
  and memory counts, and returns the current project's recent sessions and
  memories in one call. Enables the agent to orient itself at the start of
  a retrieval without multiple exploratory queries.

references/schema.md

@@ -416,6 +416,85 @@ const last5 = recent(5);
 return last5.map(s => ({ title: s.title, project: s.project_path, ended: s.ended_at }));
 ```
 
+#### `overview(opts?)`
+
+Compact orientation map for choosing the next retrieval scope. It is not an
+evidence helper: it does not return snippets, full messages, or markdown file
+contents. Passing a string is treated as `project`, and passing a number is
+treated as the current-project session `limit`.
+
+| Param | Type | Description |
+|-------|------|-------------|
+| `opts.project` | `string` | Project slug or SQL `LIKE` pattern to use as the current project scope |
+| `opts.limit` | `number` | Max recent sessions in `current_project.sessions` (default 8) |
+| `opts.projectLimit` | `number` | Max rows in the global `projects` map (default 20) |
+| `opts.memoryLimit` | `number` | Max memory records in `current_project.memories` (default 100) |
+
+If `opts.project` is absent, `overview()` tries to identify the current project
+from `process.cwd()` against `sessions.project_path`, then from exact
+`messages.cwd` matches. It does not guess the current session.
+
+**Returns:**
+
+```js
+{
+  current: {
+    cwd,
+    project: {
+      project,
+      project_path,
+      source: 'opts' | 'cwd_project_path' | 'cwd_messages',
+      confidence: 'exact' | 'inferred' | 'unknown'
+    } | null
+  },
+  current_project: {
+    project,
+    project_path,
+    session_total,
+    sessions: [
+      { id, title, project, project_path, started_at, ended_at, git_branch, message_count }
+    ],
+    memory_total,
+    memories: [
+      { id, path, summary, session_id, project, created_at }
+    ]
+  } | null,
+  projects: [
+    {
+      project,
+      project_path,
+      session_count,
+      memory_count,
+      last_session_at,
+      last_memory_at,
+      recent_branches
+    }
+  ],
+  totals: { projects, sessions, memories }
+}
+```
+
+Use `current_project.sessions` as recent entry points only. `session_total` and
+`memory_total` tell you whether the returned arrays are complete enough for the
+task. Confirm facts with `memories()`, `search()`, other helpers, or `sql()`.
+
+```js
+const map = overview({ limit: 5 });
+return {
+  current: map.current,
+  sessions: map.current_project?.sessions.map(s => ({
+    id: s.id,
+    title: s.title,
+    ended_at: s.ended_at,
+  })),
+  memories: map.current_project?.memories.map(m => ({
+    id: m.id,
+    path: m.path,
+    summary: m.summary,
+  })),
+};
+```
+
 #### `sessions(opts?)`
 
 Query sessions with filters. For backward compatibility, passing a number is treated as `limit`.