docs(15128): Phase 1 FTUE — TEA leak cleanup + Ink migration guide

[beorn]

Phase 1 of the silvery docs reorg (km @km/silvery/15128-docs-reorg).

Goal: Make README → homepage → quick start a seamless 60-second journey. Zero TEA-as-shipped wording. Give Ink users an obvious migration path.

Scope — 9 files

Homepage + packages tables (4 files)

• `docs/index.md` — Coming bullet: `@silvery/create` → `Silvertea (ships as @silvery/create)`; packages table: mark `@silvery/create` `(coming soon)`.
• `README.md` — packages table + Coming bullet: same treatment.
• `docs/about.md` — packages table: same treatment.
• `docs/reference/packages.md` — Power-User Imports block: drop `createSlice/createStore` example; add `::: tip Coming soon` for `@silvery/create`.

Drop-in Ink migration guide (1 new file)

• `docs/getting-started/migrate-from-ink.md` — drop-in story at top (`bun remove ink && bun add silvery react` + `from "ink"` → `from "silvery/ink"`). 918/931 Ink 7.0 tests pass. Walks through what's the same, what's different (13 intentional design choices), what you can opt into later. Refers into the existing `silvery-vs-ink` deep-dive.

Replace unshipped `createApp()` examples (2 files)

• `docs/guide/find.md` — replace `pipe(createApp(store), withFocus(), …)` activation example with shipped `render().run()`; add Coming Soon note for Silvertea composability.
• `docs/guide/scope.md` — 3 `createApp(store)` examples replaced with shipped `render().use(withScope("app")).run()`. Silvertea `pipe()` form kept as explicit "Coming soon" code blocks so the design narrative isn't lost.

Gate state-management.md (2 files)

• `docs/guides/state-management.md` — prominent `::: danger` banner at top declaring Silvertea unshipped; points readers at `useState` / `useReducer` / Zustand for today.
• `docs/.vitepress/config.ts` — remove "State Management" from sidebar + nav; add "Migrate from Ink" under Getting Started in both.

Verification

• `bun run docs:build` — succeeds. `migrate-from-ink.html` builds. The 10 pre-existing glossary anchor warnings into `/guide/silvery-vs-ink#rendering` etc. are not introduced by this PR.
• Migration guide appears in the sidebar under Getting Started, right after Quick Start.
• README + about.md + index.md + reference/packages.md all say "coming soon" on `@silvery/create`.
• No live `createApp()` examples remain in find.md / scope.md (kept only inside explicitly-labeled Coming Soon blocks).

Reader-facing before/after

Homepage "Coming" section

Before:

• @silvery/create — structured state management with commands, keybindings, effects-as-data

After:

• Silvertea — structured state management with commands, keybindings, effects-as-data (ships as `@silvery/create`)

README packages table

Before:

| `@silvery/create` | Composable app builder — `pipe()` providers |

After:

| `@silvery/create` | Composable app builder — `pipe()` providers (coming soon) |

Getting Started sidebar

Before:

Getting Started
Quick Start

After:

Getting Started
Quick Start
Migrate from Ink