Fix low-severity audit findings across hooks, contexts, and DX

[ConsoleTVs]

Summary

Third and final PR from the deep audit of the router library, addressing all low-severity findings (10 fixes, 10 new tests bringing total to 231).

Naming & Clarity

• Renamed PropsContext to ParamsContext for clarity across 5 import sites
• Renamed Router internal parameter from options to props
• Changed NotFound component from <div> to <h1> for semantic HTML

Developer Safety

• useParams, usePathname, useNavigationType, and useNavigationSignal now throw descriptive errors when used outside their provider instead of silently returning defaults
• Added null guard in useActiveLinkProps for updated PathnameContext sentinel

Memory Navigation Completeness

• Added back(), forward(), traverseTo(), updateCurrentEntry() stubs to createMemoryNavigation (throw with descriptive "not supported" messages)

Documentation & Exports

• Added @example JSDoc blocks to all 8 public hooks that were missing them
• Added clearPrefetchCache(matcher) exported function for cache invalidation

Code Hygiene

• Fixed extractPathname falsy check (!url → url === null || url === undefined) to allow empty strings
• Removed unused StartTransitionFn type export from TransitionContext
• Removed stale src/react-old/** and src/old/** patterns from .oxlintrc.json

Breaking Changes

PropsContext renamed to ParamsContext

What changed: The exported React context PropsContext is now ParamsContext.

Migration:

// Before
import { PropsContext } from "@studiolambda/router"

// After
import { ParamsContext } from "@studiolambda/router"

Why: The context holds route params, not React props — the old name was misleading.

StartTransitionFn type removed

What changed: The StartTransitionFn type is no longer exported from TransitionContext.

Why: It was unused and the module already exports TransitionFunction which serves the same purpose.

Hooks throw outside provider

What changed: useParams, usePathname, useNavigationType, and useNavigationSignal now throw when called outside a <Router>.

Migration: No change needed if hooks are already used inside a <Router>. If you relied on default values outside a provider, wrap the component in a <Router>.

Why: Silent defaults masked integration bugs where components were rendered outside the router tree.