docs: 1.0 documentation restructure

Split root CLAUDE.md into 19 per-directory files scoped to their source area.
Roll v0 history into docs/ARCHIVE.md; retire CONTEXT.md, CONTEXT-ARCHIVE.md,
PLAN.md, COMPLETED.md. Move plan docs under docs/. Rescue 9 live deferrals
into docs/TODO.md.

src/core/util/CLAUDE.md

@@ -0,0 +1,19 @@
+# src/core/util — small shared pure utilities
+
+## Scope
+
+Tiny, dependency-free pure helpers linked by both artifacts: whole-file byte
+loading and unit-interval clamping.
+
+## Modules
+
+- `file_bytes` (`core/util`) — the ONE whole-file byte loader (Q-W1), linked by both artifacts; blocking I/O, off-audio-thread only.
+- `clamp01` (`core/util`, header-only) — the ONE unit-interval clamp (Q-W1), replacing four per-module static copies; NaN passes through unchanged rather than collapsing to a bound.
+
+## Gotchas
+
+- `clamp01` lets NaN pass through unchanged rather than collapsing it to a bound —
+  this is deliberate (it replaced four per-module static copies that already
+  behaved this way); don't "fix" it to clamp NaN to 0 or 1.
+- `file_bytes` does blocking I/O — off-audio-thread only, never call it from
+  `process()`.