Add HTTP API docs markdown emitter with literal type support

[Copilot]

New @typespec/http-api-docs emitter that generates markdown reference documentation for HTTP-based TypeSpec services, including synthetic JSON request/response examples.

Emitter (packages/http-api-docs)

• Traverses HttpService/HttpOperation via @typespec/http, emits structured markdown with service metadata, operation signatures, parameter tables, request/response body examples, and property documentation
• Auto-generates JSON examples from TypeSpec types: models, scalars, enums, arrays, unions, nested objects, with circular reference protection
• Supports {service-name} interpolation in output filename

Type resolution and example generation

Handles all TypeSpec type kinds including literal types ("String", "Number", "Boolean"), which are distinct from their scalar counterparts:

model Config {
  kind: "standard";   // String literal → example: "standard"
  code: 200;          // Number literal → example: 200
  active: true;       // Boolean literal → example: true
}

Build integration

• Added to tsconfig.ws.json project references for watch/incremental builds
• Already autodiscovered by pnpm build:all (workspace glob) and pnpm test (vitest project glob)

Test coverage

19 tests covering service titles, HTTP verbs, path/query parameters, request/response bodies, nested models, arrays, enums, optional properties, date/boolean scalars, multi-operation APIs, @doc propagation, and string/numeric/boolean literal types.

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In general, to correctly escape strings for a markdown table cell, you must escape all characters that have special meaning in that context, including the backslash itself. If you escape | but not \, then any existing backslashes can change how following characters are interpreted (e.g. \| could become a literal | again), so the escaping is incomplete.

The best targeted fix is to extend escapeForTable so that it first escapes all backslashes by doubling them, then applies the existing transformations: converting newlines to <br> and escaping | as \|. The order matters: we must escape \ before introducing any new backslashes (like the ones used to escape |), so we don’t re‑escape them or alter the intended sequences. Concretely, in packages/http-api-docs/src/emitter.ts, update escapeForTable at line 401 to:

1. First replace all \ with \\ using a global regex.
2. Then replace newlines with <br>.
3. Then escape | with \|.

No new imports or helpers are required; this is a simple change to the existing one‑liner.

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