No Minimum Heading Depth Control

Problem

While max_depth is supported, there's no min_depth option to exclude top-level headings (e.g., only include H2 and below).

Use Case

Users may want to exclude H1 headings from the TOC since H1 is typically the document title.

Implementation

Should mirror the existing max_depth logic but filter headings below the minimum level.

Priority

Medium - Common feature in vim-markdown-toc and VSCode markdown-toc

Related

Part of the gaps analysis - see GAPS_ANALYSIS.md Quick win - mirrors existing max_depth logic