New-task drafts were keyed `new-task:<environmentId>:<projectId>`, one slot
per project, so starting a new task in a project always landed in whatever
draft already sat there and there was no way to hold two ideas for the same
repo. Web mints a draft id per draft and never had this limit; with drafts
now listed in the mobile thread list the single slot became visible.

Drafts are keyed `new-task:<draftId>` and carry their project in a
`project` stamp (environment, project, createdAt). Legacy project-keyed
entries are rewritten on load, so nothing on users' devices is lost. Each
New Task entry mints a fresh draft; tapping a Draft row resumes that draft
by id via a new `draftId` route param. Switching projects mid-compose
retargets the same draft (text and mode choices follow, branch/worktree
are cleared) instead of copy-if-empty across keys. A rejected pending task
restores into its own message-keyed draft rather than merging into
whatever the user is typing. Drafts list newest first by their own
createdAt instead of a render-time stamp.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>