Add-project: typeable, browsable destination path (create-if-missing, per environment) instead of an OS folder dialog #609

What T3 does

Add Project is a typed path with an in-app browser, not an OS folder dialog. The palette keeps a query that is simultaneously the path input and the browse cursor: getAddProjectInitialQuery seeds it with ~/, filterFilesystemBrowseEntries lists the directory server-side, arrow keys descend (appendBrowsePathSegment), and Enter on a path that does not exist still works because project.create carries createWorkspaceRootIfMissing: true (apps/web/src/components/CommandPalette.tsx:1771, packages/contracts/src/orchestration.ts:642).

The clone flow reuses that same control for step 2 instead of inventing a dialog: once a repository is chosen, the repo folder is pinned onto the browsed path, so the proposed destination reads <folder you are browsing>/<repo> live (getCloneDestinationPath, getCloneDestinationBrowsePath, packages/client-runtime/src/operations/projects.ts:216-248). Picking a directory that already has the repo's name uses it directly rather than producing repo/repo. Validation is shared with manual add: ~ expansion, explicit-relative paths need an active project, Windows-style paths rejected off Windows (resolveAddProjectPath).

Because the browse is an RPC against the environment, the same UI works for a project on a remote machine. A native dialog cannot do that.

Solenta today

projects:addViaDialog (electron/ipc.js:263) opens dialog.showOpenDialog and passes result.filePaths[0] to addProject. That is the whole flow. Consequences:

• Cannot add a path that does not exist yet (no create-if-missing) except through the separate createProject mkdir + git init path.
• Cannot type or paste a path, cannot use ~.
• Cannot browse anything but the local machine's filesystem, which blocks project add for Headless server mode and SSH remote environments #245 (headless server / SSH environments) by construction.
• Nowhere to hang a clone destination step for Clone from URL and publish a local repo in add-project #459.

Why it matters

This is the prerequisite for two things we already want. #459 needs a destination picker that can pin a repo folder onto a chosen parent; #245 needs any project path UI that is not showOpenDialog. Doing it once, as an IPC-backed browse, serves both, and the OS dialog can stay as a "Browse..." shortcut for the local case.

Scope suggestion

• fs:browse({environment, path}) IPC returning directories (+ a bounded frecency listing for the empty query).
• Add-project input: typeable path, ~ expansion, keyboard descend/ascend, entries filtered by what is typed, create-if-missing on submit, existing-project detection that opens the project instead of erroring.
• Keep showOpenDialog as a secondary button on local.
• Land it ahead of the clone flow in Clone from URL and publish a local repo in add-project #459 so the destination step is a reuse, not a second control.