docs/providers/libsql.md is missing the Capabilities & labels, Error handling and Usage examples sections

## What

docs/providers/libsql.md is missing three sections that every other fully shaped provider doc has: "Capabilities & labels", "Error handling", and "Usage examples".

## Where

docs/providers/libsql.md's numbered sections run: 1 Overview, 2 Architecture, 3 Design decisions, 4 Connection, 5 Query interface, 6 Schema introspection, 7 Monitoring & health, 8 Maintenance, 9 Testing, 10 Known limitations, 11 References.

Compare to docs/providers/mongodb.md, the shortest fully shaped sibling doc: sections 1 through 8 match, then 9 Capabilities & labels, 10 Error handling, 11 Testing, 12 Usage examples, 13 Known limitations & future work, 14 References.

## Expected

docs/providers/libsql.md follows the same section shape, in name and order, as its sibling provider docs, with real, libsql specific content in each new section rather than placeholder text.

## How to fix

1. Read docs/providers/mongodb.md's "Capabilities & labels", "Error handling" and "Usage examples" sections to see the expected shape and depth.
2. Check the libsql provider under src/lib/db/providers/ for its actual capability flags and error handling behavior, so the new sections describe real, verified behavior rather than invented content.
3. Insert the three new sections between the current section 8 (Maintenance) and section 9 (Testing), renumbering every section after them.

## How to check

docs/providers/libsql.md has the same section list, in name and order, as docs/providers/mongodb.md, and each new section describes libsql's actual behavior rather than generic text copied from another provider.

Compare docs/providers/mongodb.md with docs/providers/libsql.md to copy the expected section structure, then inspect the libsql provider under src/lib/db/providers/ for capability flags and error behavior. Add verified Capabilities & labels, Error handling, and Usage examples sections between Maintenance and Testing, renumbering later sections. Done means the section names and order match the sibling documentation and the new content is libsql-specific.

Written by the indexing model from the issue text.