Move docs/ package mirror into document-navigator plugin

Relocate the ~6k-file docs tree from the repo root into
plugins/document-navigator/docs/ so the plugin is self-contained and
portable. docs/superpowers/ (specs and plans) stays at the repo root.

Moved via cp+rm rather than git mv because directory rename() fails with
EPERM on this WSL /mnt DrvFs mount; git rename-detection pairs the
identical-content files at commit time.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/document-navigator/docs/foundation/data/clipboard/src/fallback/fallback.md

@@ -0,0 +1,94 @@
+# `fallback/fallback.ts`
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+
+## Purpose
+
+Legacy clipboard fallback paths used when `navigator.clipboard` is
+unavailable or rejects. Provides a hidden-textarea + `execCommand("copy")`
+write path and a paste-event-based read path. Both return the same
+`ClipboardResult` shape as the API path so the manager's call sites do
+not branch on which mechanism actually ran. The paste-event fallback is
+purpose-built for environments — older Safari, embedded WebViews, and
+permission-denied contexts — where `navigator.clipboard.readText`
+rejects but the user can paste manually.
+
+## Features
+
+- `copyTextFallback(text)` — synchronous textarea + `execCommand` copy.
+- `readTextFallback(timeoutMs)` — focus + paste-event capture with a
+  configurable timeout.
+- `dispatchSyntheticPaste(text)` — test helper that fires a synthetic
+  `paste` event on the most recent hidden host.
+- SSR-safe — both copy and read paths return
+  `CLIPBOARD.DOCUMENT_UNAVAILABLE` when `document` is undefined.
+- Off-screen, non-interactive host element so users never see the
+  textarea visibly steal focus.
+
+## Usage: Basic
+
+```ts
+import { copyTextFallback } from "@suaveplan/clipboard";
+
+const result = copyTextFallback("hello");
+if (!result.success) {
+    console.warn("legacy copy failed:", result.code);
+}
+```
+
+## Usage: Advanced
+
+```ts
+import {
+    readTextFallback,
+    dispatchSyntheticPaste,
+} from "@suaveplan/clipboard";
+
+async function readClipboardWithPasteFallback(): Promise<string | undefined> {
+    const result = await readTextFallback(2000);
+    return result.success ? result.data : undefined;
+}
+
+// Inside a test harness:
+const promise = readTextFallback(500);
+queueMicrotask(() => dispatchSyntheticPaste("from-test"));
+const result = await promise;
+```
+
+## API Reference
+
+### `copyTextFallback(text: string): ClipboardResult<string>`
+
+Stages a hidden `<textarea>` carrying `text`, selects it, runs
+`document.execCommand("copy")`, and removes the textarea on cleanup.
+Returns `{ success: true, data, method: "fallback" }` on success and a
+structured failure with `code: CLIPBOARD.FALLBACK_FAILED` (or
+`CLIPBOARD.DOCUMENT_UNAVAILABLE` outside the browser) otherwise.
+
+### `readTextFallback(timeoutMs: number): Promise<ClipboardResult<string>>`
+
+Creates a hidden textarea, focuses it, listens for the first `paste`
+event, and resolves with the `text/plain` payload carried by the event.
+Resolves with `code: CLIPBOARD.READ_FAILED` if the timeout elapses
+first and `code: CLIPBOARD.DOCUMENT_UNAVAILABLE` outside the browser.
+
+### `dispatchSyntheticPaste(text: string): boolean`
+
+Test helper. Locates the most recent hidden host (`textarea[aria-hidden="true"]`)
+and dispatches a `paste` ClipboardEvent carrying `text` as `text/plain`.
+Returns `true` when a host was found, `false` otherwise.
+
+## Implementation Notes
+
+The hidden textarea is positioned at `-9999px` and given `opacity: 0`
+plus `aria-hidden="true"` so assistive technologies skip it. The cleanup
+runs in a `finally` block — even if `execCommand` throws, the textarea is
+removed. The read fallback tracks a `settled` flag so a duplicate or
+post-timeout `paste` event cannot resolve the promise twice. The paste
+event may carry a null `clipboardData` on some browsers; the module
+falls back to an empty string in that case rather than rejecting, since
+"clipboard contained nothing" is a valid outcome. The synthetic-paste
+helper is exported to keep tests deterministic — production code never
+calls it.