Add Fiber, FiberRoot, Hook, Effect types with WorkTag, Lane, and Flags
branded types. Update core/types.ts to export hook-related types and
remove old VDOMInstance.

Add type predicates for fiber tags (isHostComponent, isFunctionComponent,
etc.) and assertion helpers for the fiber tree.

- isUpdatedQueue now vlaidates all five UpdateQueue<S> fields
- isHookState now checks all five Hook properties

- setDynamicProperty / getDynamicProperty, both now reject __proto__, constructor, and prototype keys by throwing an error, preventing prototype pollution
- isFiberRoot now validates types: containerInfo must be a non-null object
- assertTextProps error message now correctly names the actual source (pendingProps or memoizedProps) based on which one was used
- isHookState now validates that baseQueue, queue, and next are each either null or an object
- isEffectState now validates that tag is a number, create is a function, destroy is undefined or a function, deps is null or an array, and next is null or an object.

…eanup

  - Convert boolean-returning fiber tag helpers to real TS type predicates
  - Add stateNode !== null checks to host fiber type guards
  - Validate full shapes in isHookState, isEffectState, isUpdateQueue, and
    isMemoComponent instead of only checking key existence
  - Add isUpdate type guard for Update<S> shape validation
  - Tighten isTextProps to validate nodeValue is string or number
  - Tighten isFiberRoot to verify property types, not just presence
  - Guard isHTMLElement, isHTMLInputElement, isElement, isTextNode against
    missing DOM globals for SSR safety
  - Fix assertTextProps error message to report correct prop source
  - Reject prototype-polluting keys in setDynamicProperty/getDynamicProperty
  - Add JSDoc warnings to getMemoizedState/assertMemoizedState about unchecked casts
  - Rename mergeLanesUnsafe/intersectLanesUnsafe/removeLanesUnsafe to
    mergeLanes/intersectLanes/removeLanes
  - Move Host* type aliases above their corresponding type guard functions

Add Lane type operations for priority scheduling: mergeLanes,
removeLanes, includesSomeLane, and lane management utilities.

Add time-slicing scheduler with priority levels and shouldYield.
Add WIP tree management with prepareFreshStack and
createWorkInProgressFiber for double-buffering.

Add createFiber, createFiberFromElement, createFiberRoot, and
createWorkInProgress for constructing fiber nodes from elements.

Add findHostParent, findHostSibling, collectHostChildren for tree
traversal. Add effect creation, collection, and passive effect
scheduling.

Add reconcileChildFibers and mountChildFibers implementing the
two-pass key-based diffing algorithm for efficient child updates.

Add useState, useEffect, useRef, useMemo, useCallback, useReducer,
and useContext hooks on the fiber architecture. Update context module
to use fiber tree traversal for value lookup.

Add beginWork for tag-specific fiber processing during render phase.
Add completeWork for DOM node creation and effect flag bubbling.

Add commitPlacement, commitUpdate, commitDeletion for DOM mutations.
Add commitRoot orchestrating the three commit sub-phases: before
mutation, mutation, and layout.

Refactor event delegation to work with fiber nodes. Add registerFiber,
unregisterFiber, and fiber-based event routing while removing old
VDOM-based event handling.

Add performSyncWorkOnRoot, scheduleUpdateOnFiber, createRoot,
updateContainer, and flushSync. Add fiber/index.ts re-exporting
all public fiber APIs.

Add hydrateRoot and enterHydrationState for client-side hydration.
Add serializeFiberTree and dehydrateRoot for state serialization
and resumability.

Update core/index.ts, MiniReact.ts, and jsx-runtime to export
fiber-based implementations. Remove old dom-renderer, fragments,
hooks, and reconciler modules.

- Centralise all unsafe Lane/Lanes/Flags casts into src/fiber/bitwise.ts
- Implement binary min-heap scheduler (O(log n)) in src/fiber/minHeap.ts
- Wire concurrent rendering path (performConcurrentWorkOnRoot + renderRootConcurrent)
- Simplify branded types: Lanes = Lane alias, HookEffectTag = number
- Add 9 new test modules: bitwise, minHeap, typeGuards, lanes, scheduler,
  resumability, hydration, fiberUtils, commitIntegration
- Add compile-time type enforcement test (types.typecheck.ts)
- Export useMemo / useCallback / useReducer from index.ts
- Build interactive browser showcase (examples/interactive-showcase/)
- Update README: 473 tests, zero type errors, Phase 13 complete

Typecheck: 0 errors
Tests: 473 pass, 0 fail, 1,526 expects across 38 files