fix: support URLPattern modifiers (?, +, *) in non-exact parent routes

[uhyo]

Closes #205

Problem

Non-exact (parent) routes computed the consumed pathname prefix by counting pattern segments, assuming one pathname segment per pattern segment. Any URLPattern syntax where the number of matched segments can differ from the number of pattern segments (?, +, * modifiers, regex groups, wildcards) produced a wrong consumed prefix, so children received the wrong remaining pathname and the whole route tree failed to match:

// failed to match /docs/page/5 (with :section absent)
route({ path: "/docs/:section?", component: Layout, children: [
  route({ path: "/page/:id", component: Page }),
]})

// failed to match /files/a/b/meta
route({ path: "/files/:path+", component: Layout, children: [
  route({ path: "/meta", component: Meta }),
]})

Fix

Runtime (matchRoutes.ts): matchPath now returns match candidates instead of a single result.

• Simple patterns (literal segments and plain :params) keep the original segment-counting fast path, so the common case does no extra work.
• Patterns with variable-length syntax match the bare pattern (without the {/*}? suffix) against every pathname prefix, longest first. matchRoute backtracks to a shorter consumed prefix when no child matches the remainder, so /docs/:section? matches /docs/page/5 with section absent.
• Ambiguous matches prefer the longest consumed prefix (greedy), matching URLPattern's own semantics.
• SSR SKIPPED semantics are preserved: once a candidate's child is skipped, shorter prefixes aren't tried, so the server can't render a different tree than the client would hydrate.

Types (route.ts): ExtractParams now strips modifiers, regex groups, and group delimiters from param names, so path: "/docs/:section?" types params as { section: string } instead of { "section?": string } (also handles :id(\d+) and {/:section}?).

Docs: extended the README Path Patterns table with optional/repeated/regex parameter rows and a note that patterns work as prefixes on parent routes.

Tests

13 new cases: 11 runtime tests pinning ?/+/*/regex-group/brace-group behavior in parent routes (including greedy preference, backtracking, :path+ minimum-segment enforcement, and requireChildren: false fallback) and 2 type-level tests for modifier stripping. All 299 tests pass; typecheck, lint, and format are clean.

Note: pnpm build fails for the docs and example-rsc packages in the dev container with ReferenceError: URLPattern is not defined — this is pre-existing on the base commit (Node 22 has no global URLPattern) and unrelated to this change. The router package builds cleanly.

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