fix(browser): preserve funnel history in StrictMode

[chungyo]

Why

React Strict Mode replays effects with an extra setup-cleanup-setup cycle in development. The browser adapter cleanup removes the funnel step from the URL and its context and histories from history.state, so the current screen survives the first reload while its persisted state is lost. A second reload then resets the funnel to its initial step.

Closes #170.

What changed

• Restore cleanup state only when React reconnects effects on the same mounted funnel instance.
• Use the exact cleaned URL and history.state entry as a compare-and-swap guard, so another navigation or state update is never overwritten.
• Keep real unmount cleanup synchronous, preserve unrelated query, state, and hash values, and keep same-ID remounts starting from the initial step.
• Add browser unit coverage, a Next App Router reload regression test, and a patch changeset.

Verification

• pnpm --filter @use-funnel/browser exec vitest run (6 passed)
• pnpm --filter @use-funnel/browser build
• ESLint and Prettier checks for changed files
• Next 14.2.13 / React 18.3.1 App Router E2E (3 passed)
• Isolated Next 15.5.25 / React 19.0.8 regression E2E and TypeScript check
• Existing core, Next, React Router, React Router DOM, and React Navigation Native test suites