docs: add tsconfig.json support details to TypeScript page

[bartlomieju]

Adds a short "Configuring TypeScript with tsconfig.json" section to the TypeScript fundamentals page, explaining that Deno auto-detects tsconfig.json in any workspace directory that contains a deno.json or package.json, and (since Deno 2.1) auto-detects jsconfig.json when a package.json is present. Includes a short example of an existing Node.js tsconfig.json being picked up unchanged, and links to the existing ts_config_migration reference for the full list of supported fields, precedence rules, and compiler option defaults rather than duplicating that content here.

Closes #2666

[fibibot]

Blockers:

1. CI is red because deno fmt --check fails on this section — lines 314–315 (- Among tsconfig references, a more specific path…) and 343–344 ([configuring TypeScript](…) reference for a full list…) need reflowing. deno fmt runtime/fundamentals/typescript.md fixes it.
2. "Since Deno 2.1, jsconfig.json files are also auto-detected when a package.json is present." — I couldn't find a canonical source for the 2.1 version claim (the existing runtime/reference/ts_config_migration.md doesn't mention jsconfig.json at all). Can you link to the Deno PR or release notes that added this, or soften the version assertion?

Content otherwise mirrors runtime/reference/ts_config_migration.md lines 98–138 — same auto-detection paragraph, same supported-fields block, same precedence rules. Fine to surface this on the fundamentals page, but the two pages will need to be kept in sync going forward.

• nit: precedence list drops one rule from the reference page ("A reference takes precedence over its referrer.") — intentional simplification or oversight?