feat: implement AST approach for TypeScript parsing

[metonym]

Closes #12

Summary

This changes sveld to preserve and use TypeScript-authored prop types from .svelte components without requiring JSDoc as the primary source of truth.

The parser now keeps raw lang="ts" source for metadata extraction, indexes local TS declarations/imports, and passes internal writer-only metadata so .d.ts output can preserve canonical $props() types while JSON output remains stable.

What Changed

• stopped preprocessing away TypeScript before metadata parsing
• strip only the top-level <style> block for parsing
• added TS declaration indexing in ComponentParser
• preserve canonical props type info for typed $props() declarations
• support:
  • typed legacy export let
  • local interface / type aliases
  • intersections
  • typed whole-object $props()
  • imported type references in emitted .d.ts
• keep positional snippet renders as props-only instead of inventing slot metadata
• dedupe Snippet imports in emitted declarations
• documented type precedence and AST-only limitations in the README

Behavior Notes

Type precedence is now:

1. explicit TypeScript annotation
2. explicit JSDoc annotation
3. initializer inference
4. any

This remains AST-only support. Imported or opaque whole-object $props() types can be preserved in emitted .d.ts, but they are not always expandable into JSON metadata.

Before (Svelte 5 TypeScript)

Given:

<script lang="ts">
  interface NoticeProps {
    message: string;
    tone?: "info" | "warning";
  }

  type ActionProps = {
    onconfirm?: (detail: {
      message: string;
      tone: NoticeProps["tone"];
    }) => void;
  };

  let {
    message,
    tone = "info",
    onconfirm,
  }: NoticeProps & ActionProps = $props();

  function handleClick() {
    onconfirm?.({ message, tone });
  }
</script>

<button
  type="button"
  class:tone-warning={tone === "warning"}
  onclick={handleClick}
>
  {message}
</button>

Output (before)

import { SvelteComponentTyped } from "svelte";

export type ButtonRunesProps = {
  /**
   * @default undefined
   */
  message: string;

  /**
   * @default "info"
   */
  tone?: "info" | "warning";

  /**
   * @default undefined
   */
  onconfirm?: (detail: { message: string; tone: NoticeProps["tone"] }) => void;
};

export default class ButtonRunes extends SvelteComponentTyped<
  ButtonRunesProps,
  Record<string, any>,
  Record<string, never>
> {}

Output (after)

import { SvelteComponentTyped } from "svelte";

interface NoticeProps {
  message: string;
  tone?: "info" | "warning";
}

type ActionProps = {
  onconfirm?: (detail: { message: string; tone: NoticeProps["tone"] }) => void;
};

type $Props = NoticeProps & ActionProps;

export type TypeScriptPropsRunesProps = $Props;

export default class TypeScriptPropsRunes extends SvelteComponentTyped<
  TypeScriptPropsRunesProps,
  Record<string, any>,
  Record<string, never>
> {}