refactor(git-remotes): retrofit to the ADR-0020 context contract

Description 582 -> 237 chars, body 1217 -> 290 words. The single remotes.md
splits into config, fetch, push, and pull flow files.

Restores the confirm: true token to the force-push gate -- it is the git
plugin's cross-skill contract, gated on by git-orchestrate and git-branches.
Moves push.md's worked example off main, which the skill's own Step 1
refuses, and restores the never-bare---force directive.

plugins/git/.apm/skills/git-remotes/references/fetch.md

@@ -0,0 +1,29 @@
+---
+topic: fetch
+source_keys:
+  - git-scm-fetch-docs
+  - context7-git-htmldocs
+---
+
+# Fetching
+
+Fetch updates remote-tracking branches (`refs/remotes/<name>/*`) and never modifies a local branch, so it is always safe to run.
+
+- **One remote**: `git fetch <remote>` — all branches
+- **One branch**: `git fetch <remote> <branch>` — the result lands in `FETCH_HEAD`, not a tracking ref
+- **All remotes**: `git fetch --all`
+- **Prune properly**: `git fetch --all --prune --prune-tags` cleans stale branches *and* tags
+- **Auto-prune**: `git config --global fetch.prune true` (or `remote.<name>.prune` to scope it to one remote), and `fetch.pruneTags true` for tags
+
+## Shallow and partial fetch
+
+```bash
+git fetch --depth=<n>             # deepen history, or create a shallow clone
+git fetch --unshallow             # convert a shallow clone to full history
+git fetch --update-shallow        # allow the fetch to update the shallow boundary
+git fetch --refmap='' <remote> <branch>  # fetch without updating any tracking ref (FETCH_HEAD only)
+```
+
+## Default fetch refspec
+
+The default is `+refs/heads/*:refs/remotes/<name>/*`. The leading `+` forces the update — remote-tracking branches always mirror the remote exactly and offer no protection for local history.