fix(core/markdown): compact tight nested lists

[kitlangton]

Summary

• Add a regression covering tight multi-level nested lists rendered with the OpenCode internalBlockMode: "top-level" and streaming: true configuration.
• Normalize trailing newlines for tight-list text children as well as loose-list paragraph children.
• Inline the now-unnecessary list-child wrapper once both token shapes share the same normalization.

Why #1094 Did Not Cover This

#1094 fixed the blank-row symptom for a loose nested list whose source contains a blank line before its child list. Marked represents that parent content as a paragraph token.

This reproducer uses a tight nested list with no source blank line. Marked represents the same parent-content position as a text token. The existing normalization applied only to paragraph, leaving the trailing newline on text and producing an empty rendered row before each nested list.

Before

- Main section:

  - Supporting point:

    - Third-level detail
    - Another detail with emphasis
  - Another supporting point:

    1. First numbered item
    2. Second numbered item:

       - Nested bullet beneath a numbered item
- Second section:

  - Short detail
  - Lead-in item:

    - Explanation below the lead-in

After

- Main section:
  - Supporting point:
    - Third-level detail
    - Another detail with emphasis
  - Another supporting point:
    1. First numbered item
    2. Second numbered item:
       - Nested bullet beneath a numbered item
- Second section:
  - Short detail
  - Lead-in item:
    - Explanation below the lead-in

R/G/R Verification

• RED commit 2b03ee50 adds only the regression test; against v0.2.15 it fails with six inserted blank rows matching the Before output.
• GREEN commit 3833b39d applies the minimal normalization fix.
• REFACTOR commit fec798d4 removes getListChildMarkdownRaw, which no longer carries distinct behavior after both textual child token shapes normalize identically.
• bun test src/renderables/__tests__/Markdown.test.ts on the runnable v0.2.15 worktree: 138 pass, 0 fail.
• bun run fmt:check packages/core/src/renderables/Markdown.ts packages/core/src/renderables/__tests__/Markdown.test.ts passes.

The v0.2.15 validation seam is intentional: it is the shipped OpenTUI version currently consumed by OpenCode. Current main has an unreleased native ABI change (getRenderStats) that prevents running the TypeScript renderer suite against the published 0.2.15 dylib in a clean worktree.