refactor(url): split client and Metro URL ownership

[thymikee]

Parent: #2129

Blocked by: none. Wave 1; this is a proven multi-owner pure URL split, not a new common utility.

Scope — exact tracked files

Production:

• src/utils/url.ts

Tests:

• src/utils/__tests__/url.test.ts

Destination and importer edits

Split by owning behavior:

• normalizeBaseUrl -> src/client/base-url.ts
• buildBundleUrl -> src/metro/bundle-url.ts

Move the existing normalization tests to src/client/base-url.test.ts and add the bundle URL cases beside src/metro/bundle-url.test.ts; delete the old utility test rather than retaining a shared test path.

Update exact production importers:

• src/client/client-companion-tunnel-worker.ts -> src/client/base-url.ts
• src/client/client-companion-tunnel.ts -> src/client/base-url.ts
• src/metro/client-metro.ts -> both owning modules
• src/sdk/metro.ts -> re-export the two functions from their owning modules

Do not create src/common, a generic URL package, an internal barrel, or a compatibility re-export at src/utils/url.ts.

Behavior invariants

Preserve removal of all trailing slash characters, empty-root handling, preservation of all other URL characters, URL parsing/serialization, platform/dev/minify query values, and existing SDK exports. Preserve companion tunnel base URL normalization and Metro bundle URL behavior exactly.

Focused validation

Run:

• pnpm vitest run src/client/base-url.test.ts src/metro/bundle-url.test.ts
• the existing companion-tunnel and Metro tests
• the SDK type/build checks
• pnpm check:affected --run

Planted-red proof

No new structural rule is added. Temporarily retain one trailing slash or change a bundle query value and observe the moved tests fail independently; restore the exact behavior before the green run. The SDK export check must prove the public names resolve from their owners, not from a hidden shim.

Dependency order

Wave 1. This child is independent of the other owner slices. The terminal child is blocked by it.

Shrink target

Delete src/utils/url.ts and its old test. Split the two behaviors without duplicating normalization logic; after discounting the physical move, production LOC must not grow and no new top-level shared zone may be introduced.