fix(gh-aw): Connect mode bootstrap never resolves remote squads #1627

Bug

The shared/squad.md bootstrap always runs squad init --preset default locally. It has no logic to read .squad/config.json or fetch from a squadSource URL. A connected repo would just get the default scaffold, not the remote squad.

Found by: GPT-5.4 code review on PR #1622
Severity: High

Expected Behavior

When .squad/config.json exists with mode: "connect" and a squadSource field, the bootstrap should fetch squad files from the remote source instead of running local squad init.

Current Behavior

Bootstrap always runs squad init --preset default regardless of existing config.

Fix Options

1. Add a conditional in shared/squad.md activation steps: if .squad/config.json exists with squadSource, fetch from remote instead of running squad init
2. Add --mode connect --source {url} support to the squad-init composite action
3. Document that Connect mode requires the bootstrap to handle remote resolution (design decision needed)

Part of #1612 epic.