After New app, land on the studio's app page — the one the studio built #161

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newAppSubmit in src/web/pages/apps.ts now picks its redirect from ctx.mode: a studio-mode reader lands on repoBase(repo) (which repoHome branches to the studio's app page once the record exists), a dev-mode reader still lands on ${repoBase(repo)}/app. Nothing else about creation moved — same flash sentence, same name/collision handling.

test/apps.test.ts's #138 test is split into two: one asserting the studio landing shows the app's name, URL and first-issue sentence, one asserting dev mode still lands on its own page (fails on today's code without the fix). Since studio is the forge's default mode, two other pre-existing assertions that hardcoded the old unconditional /app redirect (test/apps.test.ts's name-derivation tests and test/web-apps.test.ts's "New app creates the app" test) needed updating to match — those were the test being wrong, not new behavior.

bun test on the full forge.json check list shows the same 6 failures before and after this change (git-push-auth and posix_spawn 'git' flakiness in this sandboxed environment, unrelated to the redirect); nothing regressed.

Closes #151