Delete the decisions and design logs; scripts, rigs and xtask off the root

Iris: "remove both decisions and iris.md. I've decided to instead make
decisions when planning with agents rather than after they do things, and
they're both too long for me to wanna read, + don't cover all the
decisions I'll wanna make about the code anyways. I'll just naturally run
into things for now. Todo is important though."

So docs/DECISIONS.md (850 lines) and docs/IRIS.md (1,986) are gone, and
AGENTS.md now says not to start another: raise a choice while planning it
with her, otherwise decide it and put the reasoning at the code it
governs. The TODO lists stay. docs/SUBAGENTS_DECISIONS.md went with them
-- same artefact, same reasoning, and she did not name it, so its six
decisions were folded into docs/SUBAGENTS.md rather than deleted.

Deleting the logs left ~30 citations dangling in code comments and docs.
Each states its reason inline and cited the file only for provenance, so
they now read "decided 2026-09-07" or name the module doc that carries
the reasoning.

The root had six things that were not a program or a document. Moved,
per "I only meant top level sh files":

  run-tests.sh, test-wg-tunnel.sh, wg-setup-host.sh  -> scripts/
  rigs/                                              -> scripts/rigs/
  xtask/                                             -> scripts/xtask/

A project's own scripts stayed with the project: app/*.sh, app-rust/*.sh,
iris/*.sh and server/enroll-link.sh did not move.

`target/` at the root is deleted and cannot come back: there was never a
workspace there, and the 29 MB was only xtask's scratch space, now in
scripts/xtask/target/. `cargo xtask apk` still runs from the repo root
and now publishes to scripts/build/outputs/apk/<mode>/ -- one directory
deep, because that is what Dev Updater's `*/build/outputs/apk/*/*.apk`
discovery pattern needs, and scripts/xtask/build would have been two.

Verified: ./scripts/run-tests.sh and `cd iris && cargo test` green, clippy
and fmt clean everywhere, `cargo xtask apk debug --abi x86_64` builds and
signs an APK carrying lib/x86_64/libai_app.so at the new publish path, and
the repo root is now eleven entries with no build output among them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/androidApp/src/main/kotlin/com/example/aiapp/BenchFixture.kt

@@ -4,7 +4,7 @@ import android.content.Context
 import java.util.concurrent.CopyOnWriteArrayList
 
 /**
- * P0's benchmark gate (see docs/RUST.md and docs/DECISIONS.md's 2026-09-05 entry): an in-process
+ * P0's benchmark gate (see docs/RUST.md and the 2026-09-05 decision): an in-process
  * fake of the backend, so the `bench` build type can drive a real session screen -- the real
  * [TranscriptSource], the real fold, the real paging -- with no server and no network permission.
  *