feat(cli): add supabase notebooks push

[SaxonF]

Adds supabase notebooks push, the mirror of notebooks pull from the previous PR in this stack. Every file in supabase/notebooks/ is written to the project notebook of that name, or to a new one when the project has none.

supabase notebooks push                 # push the whole directory
supabase notebooks push <name>          # push one notebook

Behavior worth reviewing

• Read everything before writing anything. All selected files are read and decoded before the first upload, so a directory holding one unreadable notebook fails without having half-pushed the rest.
• Absent keys stay absent. Keys a file leaves out are omitted from the request rather than sent as explicit nulls, which is how favorite keeps whatever the dashboard set on a notebook whose file never mentions it. schema_version is server-owned and dropped on pull, so it never round-trips back.
• Cell identities survive. Cell ids written out on pull are echoed on push, so a cell keeps its identity across an update instead of being replaced by a copy.
• Reconciliation points the other way. Project notebooks naming no local file get the same three answers pull offers, mirrored: leave them, write them into the directory, or delete them from the project. Passing a notebook name pushes just that one and reconciles nothing.
• The copy-and-delete plan is resolved and validated before the first upload, so a push cannot half-apply a reconciliation choice.

Reviewer notes

Beyond push/, the diff re-exports deleteRemoteNotebook and NotebookNotFoundError (used only by push) and extends the shared regression suite in notebooks.integration.test.ts to run over both commands — the previous PR ran it over pull alone. The added round-trip test pulls a notebook with chart and log cells and pushes it back, asserting the request body matches what came down.

push/SIDE_EFFECTS.md records the side-effect surface.