EPBDS-16211 H3/H4: isolate the demo, re-home the engine - #63

## What changes

These are the two findings that #151 recorded and left for a change of
their own. Both are in `docs/UPGRADE-PLAN.md`.

### The orphan scan in Appendix B reads TypeScript again

**It had checked no component since the TypeScript migration.** It
looped over `src/core/components/*.js`, and the pack has no `.js` file
now: it has 42 `.ts`/`.tsx` files.
- **In zsh**, the glob fails: `no matches found:
src/core/components/*.js`, and nothing is printed.
- **In bash**, the loop runs once, on the literal pattern. It prints one
line, `198 *`: the pattern becomes `/*'`, which matches every file that
contains a `'`.

**The new command finds the pack's `.ts` and `.tsx` files** and strips
either extension. It matches an import in either quote style, and leaves
out the component's own file under either extension.

How I checked it:
- **Run as the plan prints it,** in bash and in zsh, it scans all 42
files, with the same output in both shells.
- **It reports nothing as an orphan today:** no pack file reads 0.
- **It can still fail:** a file I planted in the pack with no importer
read 0. I then deleted it.

**Its notes on reading the output are re-measured.** The old ones
described what the scan showed on 2026-09-17:
- **`index`** used to be "the only remaining 0". It now reads 5, and
none of the five is the pack's barrel: three import the engine's
`index`, and two are doc comments. The barrel itself is imported by
directory path (`from '../components'`), which the pattern cannot see.
- **The same-name trap still applies, with a current example.** `files`
reads 5, and two of the five import `modules/variables/files.ts`. The
old example, `Tabs`, went with the H6 rename.
- **A count includes the demo.** `StandaloneTabs` reads 1, and that one
importer is the demo's `NavTabs`.

### Appendix A's structure facts

Each fact that is gone is struck through and followed by the change that
removed it, as the plan marks its other closed items:
- **The engine ⇄ form-modules cycle** went with #69 (§9.3 step 2,
2026-09-23).
- **`components/Text.js:4` importing `modules`** went with #64 (H5,
2026-09-23). The layer lint rejects both of these imports now.
- **The demo entries at the `src/` root** moved to `src/demo/` with #63
(H3, 2026-09-23).

Two more fixes in the same bullet:
- **The orphan-scan result** is the re-run above. It used to say the
barrel read 0.
- **The engine `TabList`'s path** now also gives its current one,
`src/core/engine/components/TabList.tsx`. This one was not in #151's
list.

There is no code change.

## Gates

All exited 0 on this branch, `test:coverage` on its second run:
- `lint:js`, `lint:css`, `typecheck`, `typecheck:contract`;
- `docs:props:check`, `docs:views:check`, `css:fixture:check`;
- `test:env-flags`, `build`;
- `test:coverage`, thresholds included;
- `test:pack`, `test:pack:peers`, `test:types`;
- `test:react16`, `test:react17`, `test:react19`, 2854 tests each, with
no worker crash;
- `test:e2e`, 41 tests;
- the manifest contract.

**The first `test:coverage` run failed one test, and this PR is not the
cause.** `examples.strict-mode.test.js` compares each example's DOM
after an edit, with and without StrictMode. On `tableForm` the two runs
read different DOM:
- the plain run read the date picker still open, with the typed text;
- the strict run read it closed, with the value reverted.

This is the same kind of race #149 fixed, through animation frames
instead of timers:
- The picker opens, aligns and closes on animation frames, through
`rc-util/raf`. #149 left `requestAnimationFrame` on real time.
- The 400 ms the test waits after an edit are virtual, and they take 1–3
ms of real time. Whether a real frame lands inside them is chance. With
the test's own timer setup and no coverage, 2 of 3 plain runs had no
frame there, and read the picker open.
- With frames suppressed, both modes read the picker open. So the
comparison depends on whether a frame ran.

The rerun passed all 2854 tests. The fix belongs in the test, in a
change of its own.

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