fix(mcp): declare 2020-12 dialect for tools/list schemas

[chiliec]

What does this PR do?

Fixes #696 — every tool call against the local @pascal-app/mcp server fails on clients that enforce JSON Schema 2020-12, because tools/list declares draft-07.

The MCP SDK's McpServer builds each tool's inputSchema/outputSchema with toJsonSchemaCompat and no target, so the compat layer falls back to draft-07. There's no version bump or registerTool option that changes this. The generated schemas contain no draft-07-only keywords (definitions, dependencies, $ref), so the fix re-registers the tools/list handler after tool registration and retargets the declared $schema to https://json-schema.org/draft/2020-12/schema on the way out — the approach the maintainer outlined in the issue.

How to test

1. cd packages/core && bun run build (mcp tests import built @pascal-app/core/schema)
2. cd ../mcp && bun test

New regression test src/tools/schema-dialect.test.ts asserts the raw tools/list payload only declares 2020-12 (validating through the SDK client — as the existing contract test does — would not catch this, since the client uses the SDK's own validator).

Validation (real results)

• bun test (packages/mcp): 357 pass, 0 fail (52 files)
• New test alone: pass
• RED→GREEN: removing normalizeToolSchemaDialect(server) makes the new test fail with the raw dialect showing http://json-schema.org/draft-07/schema#; restoring it turns it green.
• biome check clean on the changed files; tsc -p tsconfig.json clean.

Screenshots / screen recording

N/A — headless MCP/server change, covered by the test above.

Checklist

• I've tested this locally (bun test)
• My code follows the existing code style (bun check)
• I've updated relevant documentation (CHANGELOG)
• This PR targets the main branch

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Note

Low Risk
Response-shaping middleware on tools/list only; behavior is covered by a regression test, though it depends on SDK-internal handler registration.

Overview
Fixes #696: MCP clients that require JSON Schema 2020-12 were rejecting all tool calls because tools/list advertised the SDK default draft-07 $schema.

After tools, resources, and prompts are registered, normalizeToolSchemaDialect wraps the existing tools/list handler and recursively rewrites every $schema URL in the listed tool input/output schemas to https://json-schema.org/draft/2020-12/schema before the response is returned—without changing schema structure (no draft-07-only keywords in play).

A new integration test asserts the raw listTools() payload only exposes the 2020-12 dialect; the Unreleased changelog entry documents the fix.

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