fix: improve Deno module resolution in Vite plugin (#3734)

## Summary

Three targeted fixes to Fresh's Vite plugin for better module
resolution, plus new test coverage.

### 1. Workspace import map resolution
Pass the importer's file URL to `loader.resolve()` so bare specifiers
from workspace member packages resolve through the correct import map —
not just the root `deno.json`.

Fixes #3654

### 2. Remote island resolution
Use `this.resolve(spec)` in the `fresh-island::` and
`fresh-client-island::` resolveId handlers (`server_snapshot.ts` /
`client_snapshot.ts`) so JSR remote islands get proper `\0deno::`
specifiers. Without this, remote islands resolved to bare specifiers
that Vite couldn't load.

Fixes #3437

### 3. Babel JSX operator precedence fix
`!ssr && id.endsWith(".tsx") || id.endsWith(".jsx")` → `!ssr &&
(id.endsWith(".tsx") || id.endsWith(".jsx"))`. The missing parentheses
caused `.jsx` files to incorrectly get Preact JSX transforms during SSR.

### Other changes
- Bump `@deno/loader` from ^0.3.10 to ^0.4.0 (needed for workspace
resolution fix)
- Bump `@astral/astral` from ^0.5.5 to ^0.5.6 (fixes `@std/async@1.2.0`
compat)
- Add dev server tests for CJS module import and maxmind CJS (#3653)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bartlomieju

deno.json

@@ -74,7 +74,7 @@
     "@std/semver": "jsr:@std/semver@1",
     "@std/streams": "jsr:@std/streams@1",
 
-    "@astral/astral": "jsr:@astral/astral@^0.5.5",
+    "@astral/astral": "jsr:@astral/astral@^0.5.6",
     "@marvinh-test/fresh-island": "jsr:@marvinh-test/fresh-island@^0.0.3",
     "linkedom": "npm:linkedom@^0.18.10",
     "@std/async": "jsr:@std/async@^1.0.13",