[FEATURE] @ file autocomplete should support nested subdirectory traversal

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When using @ to reference files in the CLI, autocomplete only shows top-level items in the working directory. Typing @3_Resource/ and continuing to type does not show files inside that subdirectory.

Current behavior
Autocomplete stops at the first level. Users must type the full path manually (e.g., @3_Resource/workout.md) without any completion assistance.

Proposed Solution

Expected behavior
After typing @folder/, autocomplete should list the contents of that subdirectory, allowing users to navigate deeper paths interactively.

Why this matters
In projects or vaults with deeply nested structures, it is difficult to reference specific files without remembering exact paths. Recursive autocomplete would significantly improve the file referencing experience.

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_