Absorb: how it fits packs, flows/radar and forge-to-forge #9545

Found in the Product review of #9441.

• Packs (#9428): a pack's apps arrive as ordinary apps and a pack cannot say "absorb this one", so a forge made from a pack still needs an admin to click through Settings > Features for each. The pack parser refuses keys like env/key/data, so the shape is a boolean absorb on a PackApp that deploy applies as the deploying admin's act, with the event, never a settings value.
• Flows view and radar (#9434): radar is the first absorbed app, yet absorbed features show nowhere but the menu: no health on /system, no feed items (both "Not done yet" in the doc). Until then an absorbed app is a menu link; the Features page should say so rather than imply integration.
• Forge-to-forge: a fork of another forge's app carries its feature block, and declaring does nothing, which is right. But the Features row shows no provenance (which repository, which upstream it follows, who last changed the declaration), so an admin absorbs a stranger's menu entry blind. Settings do not travel with a fork, correctly; the doc should say so.

Change (each its own run):

• [x] PackApp.absorb?: boolean, applied at pack deploy by the admin; test beside the pack tests.
• [ ] The Features row shows provenance: repository, upstream if a fork.
• [ ] Doc: say settings stay behind on a fork; turn "Not done yet" into issues on the map.

Files: src/packs/pack.ts, src/packs/deploy.ts, src/web/pages/features.ts, docs/features/absorb.md.

Parked by the crew: the check stayed red through 2 automatic tries (pull #9699 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Reviewed pull #9759 at its head: ticked PackApp.absorb?: boolean, applied at pack deploy by the admin; test beside the pack tests.. left open: The Features row shows provenance: repository, upstream if a fork. — Not done here; it is tracked in #9770.; Doc: say settings stay behind on a fork; turn "Not done yet" into issues on the map. — The fork sentence is written, but the Not done yet list still has to become issues on the map (#9771)..

Left open after pull #9759 landed: 2 unticked items remain (The Features row shows provenance: repository, upstream if a fork.; Doc: say settings stay behind on a fork; turn "Not done yet" into issues on the map.). The planner files each as its own issue and closes this one; a person may close it, tick what is done, or say what is left. Until then the crew does not pick it again.

Both open boxes are on main: the Features page shows provenance with the upstream when a fork (provenanceRows/provenanceFacts in src/web/pages/features.ts, "Fork of" in docs/features/absorb.md), and docs/features/absorb.md says settings stay behind on a fork. Its "Not done yet" names one thing, firing a schedule, which is already on the map as #9926. Nothing is left to file; closing.