docs(agents): user-set worktree location, italic Assisted-by in PR bodies (#28805)

* docs(agents): let a user's own instructions set the worktree location

A fixed ../PX4-Autopilot-worktrees/ path overrode contributors who keep worktrees elsewhere. Their own agent instructions now win, with the sibling directory as the default.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Jacob Dahl <dahl.jakejacob@gmail.com>

* docs(agents): italicize the PR body's Assisted-by line

Set apart in italics, the disclosure reads as a footnote rather than part of the Solution section above it.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Jacob Dahl <dahl.jakejacob@gmail.com>

---------

Signed-off-by: Jacob Dahl <dahl.jakejacob@gmail.com>

.agents/README.md

@@ -13,4 +13,4 @@ Claude Code reads neither location directly. Each `CLAUDE.md` is a one-line `@AG
 | `build-px4-linux` | Board or SITL build on a Linux host |
 | `build-px4-macos` | Board build on macOS, in the `px4-dev` container |
 
-Create worktrees outside the repository, e.g. `../PX4-Autopilot-worktrees/`.
+Create worktrees where the user's own agent instructions put them. Without such a rule, put them next to the repository in `../PX4-Autopilot-worktrees/<name>/`, never inside it.

.agents/skills/build-px4-macos/SKILL.md

@@ -28,8 +28,8 @@ a flashable `.px4` artifact.
 3. Confirm Docker is available and running. Inspect the image with
    `docker image inspect px4io/px4-dev:v1.17.0`; pull it if missing.
 4. Prefer an existing worktree for a requested ref. Otherwise resolve the ref
-   (fetch its remote if necessary) and create a new detached worktree under
-   `../PX4-Autopilot-worktrees/build-<short-sha>/`, outside the repository,
+   (fetch its remote if necessary) and create a new detached worktree named
+   `build-<short-sha>` in the worktree location from `.agents/README.md`,
    using `git worktree add --detach`.
    Reuse a path only after confirming its HEAD and working-tree state match the
    request. Never switch the user's active branch.

.agents/skills/pr/SKILL.md

@@ -8,8 +8,8 @@ allowed-tools: Bash Read Glob Grep
 # PX4 Pull Request
 
 **The user is the author: no `Co-Authored-By`, no "Generated with <assistant>"
-footers. Disclose AI assistance with `Assisted-by: <tool>:<model-id>` as the
-last line of the PR body, as in the commit trailers.**
+footers. Disclose AI assistance as the last line of the PR body, italicized:
+`*Assisted-by: <tool>:<model-id>*`, matching the commit trailer.**
 
 ## Steps