[bug] Relative paths (e.g., `../`) not resolved correctly in file references

## Problem

Using relative path syntax like `../sibling-dir/file.sql` or `../../other-project/models/` to reference files in parent or sibling directories does not resolve correctly. The agent either fails to find the file or interprets the path literally instead of resolving it relative to the current working directory.

## Expected behavior

Relative paths should be resolved against the current working directory, consistent with standard shell behavior:
- `../foo` → parent directory's `foo`
- `./bar` → current directory's `bar`
- `../../baz` → two levels up, then `baz`

## Current behavior

Relative paths with `..` are not properly resolved, causing file-not-found errors or incorrect file references.

## Steps to reproduce

1. Launch `altimate` from `/Users/me/project/subdir/`
2. Ask: _"Read the file at ../config.yml"_
3. Observe: agent fails to resolve the path or reads the wrong file

## Additional context

- This affects file references in prompts, tool arguments, and path-based commands
- Absolute paths work correctly