fix: preserve source order for shared structural slots

[Mohamed Mansour (mohamedmansour)]

Client-created repeat items can still render adjacent dynamic regions out of template order on current main. A nested <for> followed by a trailing <if> produces the conditional first, while SSR and refresh preserve the declared order.

The compiler already emits TemplateSlot.order, but $wire() previously inserted text, conditional, and repeat nodes in separate type batches. When different binding kinds shared one static insertion point, their DOM order followed the batch order instead of the template.

This change keeps each binding section explicit while using one small placement model:

• Text, Conditional, and Repeat sections create their normal direct nodes or stable anchors.
• Each queues a PendingSlot containing its parent, static reference, compiler order, node, and optional raw-HTML end anchor.
• insertPendingSlots() sorts only when slots collide, then commits all nodes after every reference has been captured from the untouched DOM.
• The comparator is shared, so client creation does not allocate a new sort closure per instance.

The reactive update path is unchanged: bindings still retain direct DOM references, with no virtual DOM and no new per-update work.

Reduced regression coverage proves:

• the exact keyed nested-loop consumer shape
• the minimal unkeyed single-assignment trigger
• both <for> -> <if> and <if> -> <for> order
• initially false conditionals activated after an existing repeat
• initially empty repeats grown before an active conditional
• empty text slots around structural bindings
• Light-DOM structural parity
• unkeyed append, prepend, middle insert, and middle delete behavior
• live shadow bindings alongside projected slot content

A shared-slot hydration benchmark keeps the high-collision shape measurable.

Validation after rebasing onto origin/main:

• pnpm test: 319 unit tests passed; 263 Playwright tests passed, 2 skipped
• focused cross-kind/raw/Light-DOM/slot matrix: 26 passed
• cargo xtask check: all phases passed