Allow special characters in Wolverine.HTTP route templates (fixes #3282)

[jeremydmiller]

Fixes #3282.

Problem

Wolverine derives the generated handler C# type name from an endpoint's route template. A route can legally contain characters that are valid in a URL path but not in a C# identifier — most notably $ in an RPC-style route like /assets/$action. The name-derivation only stripped Path.GetInvalidPathChars() (a filesystem concept), so $ survived into assembly.AddType(...) and codegen failed:

CS1056: Unexpected character '$'

Fix (A + B + disambiguator)

A — Sanitize to a valid C# identifier. In HttpChain.Codegen.determineFileName, any character that isn't a valid identifier char (letter/digit/_) becomes _, underscore runs are collapsed, and a leading digit is prefixed with _. Routes with special characters now just work — no user action needed.

B — TypeName escape hatch. All [WolverineVerb] attributes gain an optional TypeName property to set the generated type name explicitly for edge cases. The override is itself sanitized, so it can never smuggle invalid code into codegen.

[WolverinePut("/assets/$action", TypeName = "TriggerAssetAction")]
public static string TriggerAction() => "triggered";

Collision disambiguator (built in from the start). Two routes that sanitize to the same type name (e.g. /a$b and /a-b → a_b) now receive a short, deterministic FNV-1a suffix in HttpGraph, applied only to chains that actually collide. Determinism matters for TypeLoadMode.Static, where codegen-time names must match what was written to disk.

Tests (special_characters_in_route_templates.cs)

• Reproduce the original CS1056 (route + real codegen via InitializeSynchronously) — now passes.
• The generated type name is a valid C# identifier.
• TypeName override is used, and is still sanitized.
• Colliding routes get distinct names and both compile.
• The disambiguation suffix is deterministic across graph builds.

Docs

New "Special Characters in Routes" section in guide/http/routing.md covering the automatic sanitization and the TypeName escape hatch.

Verification

Full Wolverine.Http.Tests: 802 passed / 0 failed / 10 skipped — no regressions (normal routes derive the same names as before; sanitization is a superset of the old replacements). Release build clean.

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