chore(biome): point schema to local node_modules

[frankieyan]

Overview

After #106 bumped @biomejs/biome to 2.4.15, biome.json still pinned its $schema to the 2.3.11 CDN URL. The mismatch is harmless at runtime (Biome reads the config either way), but editors validating against the stale URL show outdated autocomplete, and every Renovate bump widens the gap.

We point $schema at the copy under node_modules instead, which is the pattern Biome recommends for keeping the schema in lockstep with the installed version. After this, the reference tracks @biomejs/biome automatically and we never have to touch biome.json on a dependency bump.

Reference

• chore(deps): update dependency @biomejs/biome to v2.4.15 #106 surfaced the drift (ref)
• Biome configuration docs

Test plan

• Open biome.json in an editor with Biome support and confirm $schema resolves to the 2.4.15 schema under node_modules

[doistbot]

This PR updates the biome.json configuration to point its schema to the local node_modules copy rather than a hardcoded CDN URL. This is a great maintainability improvement that will automatically keep editor autocomplete in lockstep with the installed Biome version and prevent future drift. No issues were flagged during the review.

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