Add --context flag to show surrounding source code

[naheel0]

Title: Add --context flag to show surrounding source code

Problem

Users need immediate code context to diagnose errors faster without opening an editor.

Proposed change

Implement a --context [n] option that shows n lines of code before/after the error location (requires stack parsing for file/line extraction).

Files to change

• lib/formatter.js (print source snippet when available)
• lib/stack-parser.js (if not already added)
• bin/index.js (expose --context flag)

Tasks

• Respect repo root and ignore binary files.
• Add safety checks for path traversal and very large files.
• Add tests for snippet boundaries and missing files.

Acceptance criteria

• errlens analyze --context 3 prints the requested snippet when location info is present.

Labels: enhancement, low-priority