docs: fix README drift and the broken permissions in the quickstart

[austenstone]

Stacked on #78 → #77. Base retargets to main as the chain merges.

The quickstart in the README is broken

permissions:
  copilot-requests: write
  pull-requests: write

steps:
  - uses: actions/checkout@v5

Declaring a permissions: block sets every unlisted scope to none. There is no contents: here, so actions/checkout runs with contents: none and fails on any private repo. This is the same trap that has been silently breaking copilot-labeler.yml (see #78).

Fixed: added contents: read, bumped checkout to v7, added timeout-minutes, and called the trap out directly under Installation:

Declaring a permissions: block sets every scope you do not list to none. Always include contents: read if you check out the repo, and copilot-requests: write or Copilot auth will fail.

To stop it regressing, a new readme-example job runs the quickstart verbatim with those exact job-scoped permissions and fail-on-error: true. If the documented path breaks, CI goes red.

Troubleshooting

Reworked entry 1 and added a new entry 2, because "green job, nothing happened" is the actual observed symptom and nothing in the docs explained it:

Job is green but Copilot did nothing
fail-on-error defaults to false, so a failed Copilot run still passes the step. Check the job log for a Copilot CLI exited with code ... warning, which usually means missing copilot-requests: write.

Drift

Item	Was	Now
Issue Triage link	copilot-triage.yml (does not exist)	copilot-labeler.yml
Actions Report workflow	undocumented	listed
max-turns default	5	CLI default (5) — the action sets none
copilot-version default	prerelease	latest (per #77)
copilot-config	"Copilot CLI configuration"	"merged into ~/.copilot/settings.json" (per #77)

Every relative link in the README now resolves; verified programmatically.