docs(widgets): choose a project folder for widget dev sessions with /develop

[mrgoonie]

Summary

These pages now describe how to choose a project folder for widget dev sessions with /develop, and how to take that choice back (digitopvn/clarkcant#538). The English and Vietnamese pages are updated together.

• docs/index.html and vi/docs/index.html: /develop and /develop forget are added to the slash command list.
• docs/cli.html and vi/docs/cli.html:
  • The "Where" paragraph under "Develop a widget in the conversation" now explains /develop, Choose folder… and the folder dialog.
  • It also covers typing a path in a browser or when the node is remote, the card that appears when Clark asks for a folder you have not chosen, and Clark's access to the folders you chose.
  • It says the card names the folder a path really leads to, that a choice covers every folder inside it, and that /develop forget → Forget takes it back without stopping a running session. A whole drive or the home folder can run one session but is never kept.
  • The "copy the folder / not available yet (#538)" text is removed.
• docs/api.html and vi/docs/api.html:
  • New route row: person-only POST /widget-dev/chosen-folders/forget { root } → { root, forgotten }.
  • The ROOT_NOT_OWNED folder rules now include folders the person chose, what a choice covers, broad folders that are never kept, a chosen folder replaced by a link no longer counting, and the develop card in the tool answer.
  • "Choosing a folder" covers the develop-folder card action, the resolved folder the card names and starts, and asking Clark (develop_widget choose).
  • New "Forgetting a folder" bullet covers /develop forget and the develop-folder-forget action.
  • The develop_widget action list gains choose and folders, and the forget route is listed as refused for machine surfaces.

Round-2 follow-up (matching digitopvn/clarkcant#612):

• A press keeps a folder as chosen only when the pressed path is still that folder itself, so a link swapped in after the card was drawn grants nothing; a path that is not found, relative, or a network or device path gets no button.
• develop_widget choose runs only in a turn the person sent; folders runs in any turn.
• Forget answers stillCoveredBy when another chosen folder or a configured root still holds the forgotten one, and the pages say Clark keeps access through it. A chosen folder moved away is listed as not found so it can still be forgotten.
• origin/main was merged into the branch.

Implementation: digitopvn/clarkcant#612.

Verification

CLARKCANT_SOURCE=<pinned b7f9e364 checkout> corepack pnpm build:widgets and then corepack pnpm verify: passed (typecheck, tests and build).