fix(task-input): prefill repo dropdown when starting task from sidebar "+" icon

[mp-hog]

Problem

In the Tasks sidebar each repo group header has a hover "+" button to start a new task. Clicking it did not scope the new-task screen with that repo in cloud-mode, so that tasks were started under wrong repo.

It's this relation:

Fix

Make folderId drive both selectors. A registered folder already carries both path (local) and remoteUrl (the resolved owner/repo slug), so it's a single source of truth.

New useInitialRepoSelectionFromFolderId hook + pure resolveRepoSelectionForFolder resolver:

• always prefill the local directory from the folder path
• prefill the cloud repo when the folder's remote is a real owner/repo that is a connected GitHub integration
• keep the current workspace mode when it can represent the repo, and only switch (Cloud → last-used local mode) when it can't (a local-only repo while in Cloud). The switch uses the non-persisting setter, so it doesn't overwrite the user's mode preference.

Behavior

You're in	Click "+" on…	Result
Cloud	cloud-capable repo	dropdown follows the repo; stay in Cloud
Local	dual-capable repo	directory prefilled; stay in Local (cloud repo also seeded)
Cloud	local-only repo	switch to Local; directory prefilled
—	generic New task button	unchanged — falls to last-used defaults

Testing

• Unit tests for the pure resolver, areReposReady, and the hook cover every branch incl. the loading-gate and once-per-folderId guard.
• @posthog/ui typecheck + biome clean; task-detail suite green (22/22); full @posthog/ui suite green (752/752).
• Manually with local app, + icon switches to respective repo

Known limits (out of scope)

• A cloud-only group with no registered local folder falls back to defaults (no folderId/remoteUrl to key off).
• In Cloud mode, "+" on a repo whose org is not a connected GitHub integration intentionally switches to Local (per the "switch only when the mode can't represent the repo" rule).

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 23d7727.}

[greptile-apps]

Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 2
packages/ui/src/features/task-detail/hooks/useInitialRepoSelectionFromFolderId.test.ts:241-267
**Missing "waits for folders to load" test case**

The deleted `useInitialDirectoryFromFolderId.test.ts` explicitly tested the scenario where `folders` starts empty and the target folder arrives in a later render. That case is absent from the new test file. The hook bails early when `folders.find()` returns `undefined` and intentionally leaves `dirInitRef.current` unset so the effect retries once `folders` loads — but without a test for this path, a future regression (e.g., accidentally setting `dirInitRef.current` before finding the folder) would go unnoticed.

### Issue 2 of 2
packages/ui/src/features/task-detail/hooks/useInitialRepoSelectionFromFolderId.ts:22-29
**`areReposReady` permanently returns `false` when integration exists but repos are empty**

When `hasGithubIntegration = true` and `repositoriesCount = 0` is not a transient gap (e.g., a user installed the GitHub App then revoked access to every repository), `areReposReady` never returns `true`. As a result `reposLoaded` stays `false` in the hook, `repoModeInitRef.current` is never set, and clicking "+" on a local-only folder while in Cloud mode silently leaves the user in Cloud mode. The directory prefill still fires, so the failure is partial rather than total — but the mode switch the fix promises never happens for this cohort.

_{Reviews (1): Last reviewed commit: "fix(task-input): distinguish settled-emp..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into posthog-code/pr..." | Re-trigger Greptile}