feat: ignore trailing slashes during route matching, configurable via trailingSlash prop

[uhyo]

Closes #209

Problem

/users/ never matched route({ path: "users" }) (and vice versa) — URLPattern is strict about trailing slashes, and the router did no normalization. Worse, the strictness was inconsistent: prefix (parent) routes already tolerated a trailing slash via their {/*}? suffix, so /users/ could render fine or 404 depending on whether the route happened to have children.

Changes

• Matching now ignores a single trailing slash by default. One trailing slash is stripped from the pathname and from route path patterns before matching. The root / is unaffected, only one slash is stripped (/users// is not repaired), and the URL itself is never rewritten — useLocation() still reports the pathname as-is.
• The policy is configurable via a new trailingSlash prop on <Router>: "ignore" (default) or "strict" for the previous exact-match behavior. An enum (rather than a boolean) leaves room for a future "redirect"-style canonicalization mode.
• All three match sites agree. The option is threaded through both render-time matchRoutes calls and the navigation-interception decision in NavigationAPIAdapter (via a new optional getMatchOptions getter on setupInterception), so the router never intercepts a navigation it won't render or vice versa.
• Tests pin the policy: leaf/param/nested matching with trailing slashes, pattern-side slashes, root behavior, wildcard captures excluding the slash, no fall-through to catch-alls, strict mode, and Router-level tests covering rendering, URL non-rewriting, and interception.
• Docs: new "Trailing Slashes" subsection in the Nested Routes guide and a trailingSlash row in the <Router> props table.

Release note

Default behavior changes: URLs with a trailing slash now match their slash-less route instead of falling through to a catch-all/404. Apps relying on the old strictness can opt back in with trailingSlash="strict". This should ship as at least a minor version with a changelog callout.

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https://claude.ai/code/session_011JDF1rgn26iBR7XDT9riqv

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