fix: restore markdown list markers

[matt2e]

Summary:

• Restore explicit unordered and ordered list marker styles in note and session markdown renderers.
• Add nested unordered marker styles so markdown hierarchy is visible.

Tests:

• Push hooks passed: crates-fmt, crates-test, crates-lint, differ-ci, staged-ci.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve checkbox task-list markers

When markdown contains a GFM task list such as - [ ] todo, the modal renderers run marked with gfm: true and the sanitizer explicitly allows checkbox input tags, so those lists render as checkbox tasks. This blanket ul marker rule also applies to the task-list container, making those items show both a disc bullet and a checkbox in session/note markdown; please suppress the list marker for checkbox task-list items while keeping bullets for normal unordered lists.

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