docs: document how to exclude files from deno check

[lunadogbot]

Summary

The deno check reference page didn't mention how to scope or exclude paths from type-checking — a reader asked in #2915 "How do I ignore checking files under a directory?" and the page only showed checking single files or lists of files.

Adds a short Scoping and excluding files section to runtime/reference/cli/check.md covering:

• Passing directories/globs as positional args (e.g. deno check src/, deno check "src/**/*.ts")
• Using the top-level exclude field in deno.json, which applies to deno check along with deno fmt/deno lint
• A link to the include and exclude section of the configuration reference for full glob syntax

Kept the addition focused per the issue's guidance — one section, one code block, link out to the configuration reference for the deeper details.

Test plan

• deno fmt --check runtime/reference/cli/check.md clean
• Verified the documented exclude behavior locally:

  $ echo '{"exclude":["skip/"]}' > deno.json
  $ mkdir -p skip && echo 'const x: number = "s";' > skip/bad.ts
  $ echo 'const y: number = 1;' > good.ts
  $ deno check .
  Check good.ts          # skip/bad.ts correctly excluded

• Anchor #include-and-exclude matches Lume's slug for ## include and exclude in runtime/fundamentals/configuration.md (same pattern as other in-repo links like #linting, #formatting)

cc @bartlomieju

Closes #2915
Closes bartlomieju/orchid-inbox#67

[lunadogbot]

Heads-up on the failing lint and link check run: the failure is in the "Build: main site" step with TypeError: Cannot resolve module "lume/jsx-runtime" on /styleguide/typography.mdx, which is unrelated to this PR (a markdown-only change in runtime/reference/cli/check.md). The same failure appears on every recent PR run today across many branches, including unrelated ones — looks like a pre-existing environment/build issue on main.

Verified locally on this branch:

• deno fmt --check — clean (698 files)
• deno task test — 4 passed (386 steps), 0 failed