feat: load project skills in chats - #30838

…lper

…r project

Add experimental routes to list, create, read, update and delete skills
on a chat project. Reading needs read on the project and writes need
update; callers who lack the permission get a 404 like the project
instructions routes. The handlers reuse the shared skill create and
update path, map the per-project cap and name index to 409, and audit
every write as a chat_project_skill.

Add matching ExperimentalClient methods.

Chats in a project now get the project's enabled skills as a new
"project" skill source, read as the chat owner each turn. Subagents use
the root chat's project. read_skill loads project skill bodies, and
MergeSkills takes sources in merge order so new sources do not change
its signature.

The "/" menu offers the skills of the chat's project, next to personal,
organization and workspace skills, and /clear and /compact defer to a
project skill with the same name. Documents project skills.

…g in the slash menu

Organization and project skills load through one hook, and the menu
renders its skill groups from one ordered list. Adds project loading and
error stories.

…lify skill group offsets

…nd resolve emptiness in the hook

…naming in the composer

Cover the project-only skill tool check in the integration test, the
project skill body loader's not-found mapping, and the chat-projects
experiment gate in the composer.

…gration after main

…gration after main

# Conflicts:
#	coderd/x/chatd/chatd.go
#	coderd/x/chatd/generation_preparer.go

Add experimental routes to list, create, read, update and delete skills
on a chat project. Reading needs read on the project and writes need
update; callers who lack the permission get a 404 like the project
instructions routes. The handlers reuse the shared skill create and
update path, map the per-project cap and name index to 409, and audit
every write as a chat_project_skill.

Add matching ExperimentalClient methods.

…hatd