docs: move the long-form docs into docs/, without the superpowers nesting

ARCHITECTURE, PRODUCT and TODO move out of the repository root, and
docs/superpowers/{specs,plans} flattens to docs/{specs,plans}:
"superpowers" names the tool that wrote those documents, not a kind of
document.

No content changes. This commit is the move, plus the roughly thirty
cross-references the move invalidated.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/demo-data.ts

@@ -11,7 +11,7 @@
  * profile on every run unless you pass --profile, so without this every
  * screenshot shows an app full of zeros.
  *
- * The data is visibly synthetic on purpose. PRODUCT.md: the owner's real budget
+ * The data is visibly synthetic on purpose. docs/PRODUCT.md: the owner's real budget
  * never leaves their browser, so it is never available as example material, and
  * illustrative data must not pretend to be real.
  */
@@ -19,7 +19,7 @@ import { createSeedDataset } from "../src/domain/seed.ts";
 import * as actions from "../src/store/actions.ts";
 import { FALLBACK_FX_RATES } from "../src/store/bakedRates.ts";
 
-// Visibly synthetic, per PRODUCT.md: the owner's real budget must never be
+// Visibly synthetic, per docs/PRODUCT.md: the owner's real budget must never be
 // used as example material, and illustrative data must not look real.
 const d = createSeedDataset("2026-01", FALLBACK_FX_RATES);
 const [games, food, social] = d.posts as [typeof d.posts[0], typeof d.posts[0], typeof d.posts[0]];

scripts/fetch-fonts.ts

@@ -3,7 +3,7 @@
  *
  *   bun scripts/fetch-fonts.ts
  *
- * Self-hosted, not linked from a CDN, because PRODUCT.md's position is that the
+ * Self-hosted, not linked from a CDN, because docs/PRODUCT.md's position is that the
  * app works offline and needs no third party: a font request to another origin
  * on every cold load contradicts that, and would leak the fact that the app was
  * opened. The files are COMMITTED so neither the build nor a fresh checkout

scripts/screenshot.ts

@@ -7,7 +7,7 @@
  *                             [--eval=<js>|--eval-file=<path>] [--dark] [--reload]
  *                             [--profile=<dir>] [--eval-after-file=<path>]
  *
- * Why this exists: ARCHITECTURE.md and TODO.md both say nothing here can run a
+ * Why this exists: docs/ARCHITECTURE.md and docs/TODO.md both say nothing here can run a
  * browser, so appearance has never been verified. Chrome IS available, but its
  * plain `--screenshot` flag fires on the load event — before this app's async
  * IndexedDB read resolves, which captures an empty page. Driving CDP directly