design: plugin capabilities are loaded in place, not copied

capabilities/ is meant to be forked — core's work plus the owner's, and nothing
else. Four publishers copy plugin files into it at install, so a fork
accumulates files it did not author with nothing on disk saying which. On this
machine skills/email-db/ and extensions/ are sitting untracked in that
repository right now, and there is no good answer: commit them and the fork
carries another plugin's work, leave them and git status is permanently noisy.

Copying is wrong a second way that has nothing to do with git. A copy goes
stale — plugins:update pulls new plugin code while the copied capability keeps
describing the old one — and a copy survives plugins:disable, so a disabled
plugin's skill stays in the agent's index.

So the platform reads them where they are: the capabilities directory, plus each
installed and enabled plugin's own. Nothing is copied, and nothing needs a
namespace to stay apart because separate directories already do that
structurally rather than by convention.

Four bugs stop existing: forks stay clean, capabilities update with the plugin,
disable actually disables, and uninstall needs no cleanup — so there is no list
of filenames to get wrong and delete the owner's work with.

Deletes all four publishers when built, including api/tasks/publish.ts from
earlier today, superseded before it shipped anywhere. app-store/assets stays —
those are images served over HTTP, and the copy is what makes them reachable.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: 656f5c85-e49a-4f1f-b9f3-042a04b4d043

CLAUDE.md

@@ -537,6 +537,10 @@ explaining why it was safe.
 - `docs/editor-buffer-corruption.md` — an open bug with a trap set for it: background-job output appearing
   inside a file open in the editor. Read it BEFORE investigating a report of that, and before re-testing
   anything it already rules out
+- `docs/plugin-capabilities.md` — **designed, not built**: a plugin's tasks, skills and affordances are
+  READ where they live, never copied into `capabilities/`. Why copying breaks a forkable repository, why it
+  goes stale on update and survives a disable, and why separate directories beat namespaced paths —
+  a namespace makes provenance readable, separate directories make it structural
 - `docs/filesystem-quotas.md` — **planned, not done**: the host-side half of per-user and per-team storage
   limits. Why the kernel has to enforce it rather than the platform (members have `terminal` and can write
   past anything we count), why `usrquota`+`grpquota` and not project quotas, and the one thing easiest to