feat(input): list block types + marker rendering (lists 2/5)

[wildseansy]

The list stack (per the review ask, now including ordered lists — the shared machinery made them cheap to add):

1. refactor(input): generalize empty-line anchor machinery beyond headings (lists 1/5) #510 — anchor machinery refactor (no behavior change)
2. feat(input): list block types + marker rendering (lists 2/5) #511 — list block types + marker rendering
3. feat(input): parse and serialize lists (lists 3/5) #512 — parser + serializer
4. feat(input): list commands, keyboard editing, and empty-item anchors (lists 4/5) #513 — commands + keyboard + ZWSP/empty anchors
5. feat(input): list state, toolbar, docs, and e2e (lists 5/5) #514 — state + toolbar + docs + e2e

GitHub can't base a fork PR on another fork branch, so every PR targets main and the diff shown for PR N is cumulative — this PR's own change is its last commit (each stage is exactly one commit on the previous branch). We'll merge bottom-up; after each merge the next PR's diff collapses to just its own commit. Checkout feat/list-5-state to test the full feature end-to-end.

This PR (last commit)

UNORDERED_LIST_ITEM / ORDERED_LIST_ITEM with 0-based nesting depth in the range's level payload, joined to the anchored-type set. The store's list-metadata pass clamps depths to valid ancestry (an item nests at most one level under the previous adjacent item — CommonMark cannot represent orphan nesting, so every editor state serializes losslessly) and computes each ordered item's 1-based ordinal from its position among adjacent same-depth, same-type siblings — numbering stays correct as items are added, removed, or re-nested.

Rendering: Android draws markers via LeadingMarginSpans (dot/ring/square by depth for bullets, right-aligned N. for ordered) plus a LineHeightSpan for the new listItemSpacing prop; iOS reserves the indent column via the paragraph style and draws the glyph/number in the layout manager, reading the ordinal from a stamped text attribute. One handler instance per type serves every depth, mirroring the heading handler.

The layout manager's empty-line marker API is exercised by the orchestrator in #513.

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