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.

docs/product/capture-tail.md

@@ -1,19 +1,20 @@
 # Capture tail — spec
 
 Authoritative spec for the **capture-tail** feature: preserving reverb/release
-tails that decay past the end of a capture range. The tickable milestone lives in
-`PLAN.md` (Milestone T); this doc holds the full technical detail **and** the
-product framing.
+tails that decay past the end of a capture range. The tickable milestone's landed
+history is in `docs/ARCHIVE.md` (Milestone T); this doc holds the full technical
+detail **and** the product framing.
 
-> **Why this doc carries the technical spec (not `CONTEXT.md`).** Every other
-> pillar (capture M0–M11, Design View, Multi-bank) keeps its authoritative
-> technical spec as a `CONTEXT.md §` section and its *why* in a `docs/product/`
-> note. Capture-tail is a rider on the already-shipped offline-render path
-> (M3/M7), not a standalone pillar, and it is being specced without reopening
-> `CONTEXT.md`. So the authoritative detail lands **here**, house-styled to match
-> the CONTEXT specs; when the tail work lands, doc-keeper may fold the invariant
-> deltas into `CONTEXT.md §Precision invariants` as landed history. Same standing
-> discipline applies: **verify every REAPER API name/flag against
+> **Why this doc carries the technical spec (not the architecture docs).** Every
+> other pillar (capture M0–M11, Design View, Multi-bank) keeps its authoritative
+> technical spec as a per-directory `src/**/CLAUDE.md` section and its *why* in a
+> `docs/product/` note. Capture-tail is a rider on the already-shipped
+> offline-render path (M3/M7), not a standalone pillar, and it was specced without
+> reopening the architecture spec. So the authoritative detail lands **here**,
+> house-styled to match those specs; the landed invariant deltas are folded into
+> root `CLAUDE.md` §Precision invariants and `src/core/capture/CLAUDE.md` /
+> `src/shell/capture/CLAUDE.md` as landed history. Same standing discipline
+> applies: **verify every REAPER API name/flag against
 > `vendor/reaper-sdk/sdk/reaper_plugin_functions.h` before use** — the flag values
 > below are transcribed from that header (line numbers cited) and are not guesses.
 
@@ -252,7 +253,7 @@ held to bit-identical repeats.
 - **Opt-in beyond the region.** The tail only ever adds audio past the range end
   when a tail is explicitly requested (Auto or Manual). This is exactly the existing
   invariant: *"no added silence unless a tail is explicitly requested"*
-  (`CONTEXT.md §Precision invariants`, `CLAUDE.md §Exact bounds`). Auto-trim
+  (`CLAUDE.md §Precision invariants §Exact bounds`). Auto-trim
   strengthens it — the tail added is decay, not silence, and the silence past the
   decay is trimmed off.
 - **The null test uses NO tail.** The null-test / verify capture (M10) and any
@@ -274,8 +275,8 @@ held to bit-identical repeats.
     the tail is **the track's own reverb/delay decay**, not the parent bus's. A track
     with a reverb plugin captures that reverb's tail; a track feeding a folder reverb
     does **not** capture the folder reverb's tail (that send is out of scope — and
-    note the pre-existing send-isolation caveat in `PLAN.md §Open questions`, which
-    the tail inherits unchanged, does not worsen). Correct and consistent.
+    note the pre-existing send-isolation caveat, which the tail inherits
+    unchanged, does not worsen). Correct and consistent.
   - **Item scope:** item/take FX only, self-track + ancestors + master bypassed →
     the tail is the **item/take FX decay only**. An item with a take reverb captures
     its tail; the track's reverb does not ring into it. Correct.