Add vector data analysis tutorial

[Valyrian-Code]

Adds a new beginner/intermediate tutorial on vector data analysis — the tutorial
set currently has no dedicated vector-focused tutorial, so this fills that gap and
covers the operations users reach for most often.

What it covers

Using the North Carolina schools_wake (points), roadsmajor (lines), and
zipcodes_wake (areas), it works through a single "school accessibility" example:

1. Exploring features and attributes — v.info, v.db.select
2. Selecting by attribute — v.extract (the 95 elementary schools)
3. Buffering — v.buffer (a 500 m road corridor)
4. Selecting by location — v.select (the 15 elementary schools within the corridor)
5. Overlay — v.overlay (road corridor intersected with ZIP areas)
6. Counting per area — v.vect.stats + a d.vect.thematic choropleth of schools per ZIP

Details

• Uses the standard North Carolina sample dataset and the grass.tools API (GRASS 8.5), consistent with the recent NumPy/Landlab tutorial.
• All code was run against GRASS 8.5; the figures are real outputs of the workflow, and the tutorial renders cleanly with Quarto (eval: false).
• Categories: vector, beginner, intermediate, Python.
• Cross-links to the Thematic Maps and Terrain/DEMs tutorials.

Feedback on scope, the choice of example, or wording is very welcome.

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