fix(worktrees): the injected agent skill no longer blocks removal

With Codeman Agent Skill on (agentSkillEnabled), every session create
writes the skill into the folder the session runs in, so a session in a
worktree leaves an untracked .claude/skills/codeman/ (claude) or
.agents/skills/codeman/ (codex, gemini and the rest) behind. git then
refuses `git worktree remove` for that worktree forever, and an agent
running `git add -A` there would commit Codeman's skill into its branch
(reproduced: the worktree's status showed "?? .agents/" and
"?? .claude/").

A create now excludes <skills dir>/codeman/ next to the hooks file, for
every skills folder the registry names (capabilities.agentSkillDir,
read at call time by the route and passed in as data, so no CLI id is
branched on). Like the other lines it is only added when git does not
already ignore the path, and only to the repository's local
info/exclude.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/api-reference.md

@@ -1040,7 +1040,7 @@ A local case whose folder is the top of a git repository can keep **worktrees**
 - `name`: 1 to 64 characters of `A-Z a-z 0-9 . _ -`, starting with a letter or digit, no `..`, not ending in `.` or `.lock`. `400` otherwise.
 - `branch`: the NEW branch, default `worktree-<name>`. Letters, digits, `.`, `_`, `-`, `/`, then `git check-ref-format --branch` must accept it unchanged. An existing branch is `409 ALREADY_EXISTS` (never reset), and so is a name whose folder already exists.
 - `base`: where the branch starts, default `HEAD` (the case's current commit): a branch, tag or commit, resolved before anything is written (`400` when it is not a commit, which includes an empty repository).
-- `excludeAdded` lists the lines appended to the repository's local `info/exclude` (in the real common git dir, never a tracked `.gitignore`) when git did not already ignore them: `/.claude/worktrees/`, so the main checkout does not show the worktrees as untracked, and `/.claude/settings.local.json`, the hooks file Codeman writes for every claude session, which would otherwise make `git worktree remove` refuse.
+- `excludeAdded` lists the lines appended to the repository's local `info/exclude` (in the real common git dir, never a tracked `.gitignore`) when git did not already ignore them: `/.claude/worktrees/`, so the main checkout does not show the worktrees as untracked, `/.claude/settings.local.json`, the hooks file Codeman writes for every claude session, which would otherwise make `git worktree remove` refuse, and the agent skill copy (`/.claude/skills/codeman/`, `/.agents/skills/codeman/`: every skills folder the CLI registry names) that sessions get while `agentSkillEnabled` is on, for the same reason.
 - A symlinked `.claude` or `.claude/worktrees` directory is refused (`400`): a repository cannot redirect the worktree outside itself.
 
 `DELETE /api/cases/:name/worktrees/:worktree[?deleteBranch=true]` removes a managed worktree with `git worktree remove` **without `--force`**: git refuses a worktree with modified or untracked files (or a locked one), and that refusal is the answer, `409 CONFLICT` with git's own words in `error`. A live session at or inside the worktree is `409` as well. With `deleteBranch=true` the branch is deleted with `git branch -d`, never `-D`, so an unmerged branch is kept: the response is still `200`, with `branchDeleted: false` and git's reason in `branchError`. Response: `{ removed: { name, path, branch, branchDeleted, branchError? } }`. A folder git does not list as a worktree of this repository, or a symlink in its place, is `404`/`400`. A managed worktree whose folder is gone (deleted by hand; the list reports it `prunable`) is still removable: git then only drops its record, which is what frees the name for a new worktree. A session never starts in one.