refactor(env): eliminate hardcoded .js imports via dynamic schema resolution

[benzy018]

Summary

Closes #338

Refactors @guildpass/env to eliminate hardcoded .js file extensions in source imports. Schema imports now use TypeScript syntax (.ts), so resolution no longer depends on the emitted output format, output directory layout, or the runtime emit strategy.

Changes

• packages/env/src/index.ts — schema/validate imports changed from ./schemas/dashboard.js → ./schemas/dashboard.ts (same for access-api, discord-bot, validate).
• packages/env/src/cli/index.ts — import changed from ../index.js → ../index.ts.
• packages/env/test/dashboard.test.ts — tests now import schemas from ../src/schemas/dashboard.ts and ../src/validate.ts (source-direct consumption, no emit-format coupling).
• packages/env/tsconfig.json — enabled allowImportingTsExtensions + rewriteRelativeImportExtensions. tsc rewrites .ts → .js on emit, so compiled output stays valid Node ESM.
• packages/env/package.json — bumped typescript devDependency to ^5.7.0 (minimum required for rewriteRelativeImportExtensions).

Why .ts extensions instead of no-extension + moduleResolution: "bundler"

The issue suggested extensionless imports with moduleResolution: "bundler". I tested that approach and it breaks Node ESM at runtime: tsc emits extensionless relative specifiers verbatim, so node packages/env/dist/cli/index.js and direct import("@guildpass/env") both fail with ERR_MODULE_NOT_FOUND. The repo has no bundler in the build chain (all packages compile with plain tsc), so there is no bundler to resolve those specifiers. Using .ts extensions (explicitly allowed by the issue's expected outcome: "Schema imports use TypeScript syntax (.ts or no extension)") achieves the same goal while keeping the compiled output fully runtime-safe and consistent with the existing tsc-only build.

Verification

• pnpm --filter @guildpass/env build — passes
• pnpm --filter @guildpass/env typecheck — passes
• pnpm --filter @guildpass/env test — 7/7 pass
• node packages/env/dist/cli/index.js --app dashboard — runs correctly
• Direct import("@guildpass/env") in Node ESM — resolves all exports
• apps/dashboard typecheck — unchanged (only pre-existing @guildpass/metrics errors; the @guildpass/metrics and @guildpass/contracts clean-build failures exist on main too)