Projects created before folder-linked Projects can't link a local folder — Context offers only Upload / Add text / GitHub, no migration path

## Environment

- Claude desktop app, macOS (Darwin 25.6), Projects view — observed 2026-09-09
- Project "HeartOfGold", created earlier in 2026 (originally under another name), used daily; ~10 chats, Instructions set
- Newer Projects in the same account show a linked local folder; this one does not and offers no way to add one

## Steps to reproduce

1. Open a Project created before folder-linked Projects existed.
2. Sidebar → **Context** → **+**.
3. Observe the menu: **Upload from device**, **Add text content**, **GitHub**. Nothing to link a local folder.
4. Open the Project's **⋮** menu: no folder option there either.
5. Create a brand-new Project: the folder option is offered.

## Expected

Either the same Project can be linked to a local folder after creation, or there is a first-class "migrate / duplicate with folder" action that carries Instructions, Context and Project memory across.

## Actual

The old Project is stuck in upload-only mode. The only "live source" offered is GitHub sync, which is not a substitute for repositories deliberately kept off GitHub (this one holds a home-network device inventory and is mirrored on a NAS instead).

## Impact

- Every refresh of Project context is a manual drag-and-drop of snapshots that go stale the same day; the Instructions have to warn the model that uploads may be out of date.
- CLI / Claude Code workflows can't feed the Project at all: nothing a tool writes lands in the Project, whereas a linked folder is exactly the surface they write to.
- Long-lived Projects are the ones most worth keeping (accumulated chats and memory) and the ones penalised: the only way to get the folder is to recreate the Project and lose continuity.
- Assistant sessions working from the repo naturally assume "the Project has a folder" because newer ones do — we had to write a standing rule into the repo README to stop that.

## Ask

1. Allow linking a local folder to an existing Project (same UI as at creation).
2. Failing that, a documented migration: new Project with folder, with Instructions, Context items, memory and chats moved over in one action rather than by hand.
3. Meanwhile, state in the Context "+" menu that folder linking is unavailable for this Project, so users don't hunt for it.

## Screenshots

(Added below: the Project page — Instructions, Memory, Context, Scheduled, no folder — and the Context "+" menu showing the three options only.)

No implementation files, tests, or entry points are identified in the issue. First reproduce the existing and new Project flows in the Claude desktop app, then determine which product component owns Project folder linking and migration; done means an existing Project can gain a folder or a documented migration preserves the requested data.

Rédigé par le modèle d'indexation à partir du texte de l'issue.