chore: lint core/react with eslint-plugin-react-hooks (#2192)

`eslint-plugin-react-hooks` was a `clients/web` devDependency only, and each
client's `eslint .` is scoped to its own directory — so the whole hook rule
set had never looked at `core/react/`, a directory of nothing but React
hooks. "Neither surface has JSX" was the stated reason and was never a good
one: the rules judge hooks, not JSX.

Add the plugin at the root and apply it in a `core/react/**` block (scoped
there rather than to all of `core/**`, since the rules key off the `use`
prefix), with `exhaustive-deps` promoted to `error` as `clients/web` does.

Resolve the 15 findings it then reports:

- `useSettingsDraft` / `useClientSettingsDraft` seed their draft during
  render instead of in a `targetId`/`opened`-keyed effect, so the previous
  target's values never reach the DOM — the same rule `clients/web` spells
  `useValueChange`. Their "latest value" refs move from render-time writes
  into an effect; every reader (the debounce timer, `flush`, `onChange`)
  runs after a commit, so a post-commit write is what they need.
- The three async loaders keep their effects behind justified inline
  disables: `set-state-in-effect` follows a call into an async function
  without modelling the `await`, verified against a minimal hook whose only
  setState is in a continuation.
- `useInitialConfig`'s cleanup bump keeps reading `generation.current` at
  teardown — the rule's "copy it into a variable" advice would restore a
  stale request token and let a superseded response commit.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013hzwzS8UvBsr4yZm7o7sev
Signed-off-by: cliffhall <cliff@futurescale.com>

.github/copilot-instructions.md

@@ -51,7 +51,7 @@ const CardContent = Group.withProps({
 
 ### State and effects
 
-- **Never reset or re-sync local state from a prop inside a `useEffect`.** `useEffect(() => setX(prop), [prop])` paints the stale value first and renders twice; it is an error under `react-hooks/set-state-in-effect`.
+- **Never reset or re-sync local state from a prop inside a `useEffect`.** `useEffect(() => setX(prop), [prop])` paints the stale value first and renders twice; it is an error under `react-hooks/set-state-in-effect` — enforced in `clients/web`, `clients/tui`, and `core/react/**` (#2192). The same rule set forbids writing a ref during render (`react-hooks/refs`): sync a "latest value" ref in an effect instead.
 - Use **`useValueChange(value, onChange)`** (`src/hooks/useValueChange.ts`) — React's documented "adjusting state during render" pattern. It does not fire on the first render; seed the state with `useState`. The comparison is `Object.is`, so pass a **referentially stable** value — a primitive key (id/name/URI) or a memoized one, never a fresh object literal.
 - The `onChange` runs **during render**, so it must be pure — `setState` and nothing else. No fetches, DOM writes, logging, ref mutation, or parent callbacks; a render can be replayed or abandoned.
 - Effects remain correct for real external-system synchronization (DOM measurement, rAF, subscriptions, timers).