docs: fix CONTRIBUTING branch baseline and require dogfooding the public team repo

Summary

.github/CONTRIBUTING.md is wrong on the default branch, and it never asks CLI contributors to run TeamAI against a TeamAI team repo (dogfooding / bootstrap).

Problems

1. Wrong branch. "Making a Change" tells people to create a feature branch from master. The default branch of this repo is main (origin/HEAD → refs/heads/main).
2. No dogfood setup. Contributors only npm install / npm link. They never teamai init a team repo, so they do not exercise pull, hooks, recall, or the contributor path while developing the CLI.

Proposed docs-only change

Update .github/CONTRIBUTING.md only (README already links there). No new CLI commands.

Branch baseline

• Create feature branches from the latest origin/main.
• Prefer a git worktree for code changes, matching existing maintainer practice.

Required dogfood (all contributors)

Create a regular (not template) public team repo under teamai-hub, e.g. https://github.com/teamai-hub/teamai-cli-dev, with main branch protection (PR + review). Put only public-safe skills / rules / docs there.

In the CLI clone (not as teamai init .):

npm run build && npm link
teamai init https://github.com/teamai-hub/teamai-cli-dev --scope project --role dev
teamai pull
git status   # nothing under .teamai/ or tool dirs should be staged for this repo

Document these pitfalls:

• Init the canonical hub URL, not a personal fork. teamai init <url> treats that URL as the team repo; a fork diverges immediately, and GitHub push/PR today targets the configured remote (no fork-to-upstream flow).
• Do not run teamai init .. That is single-repo mode: it turns the CLI source tree into the team repo and writes scaffolding at the repo root (easy to commit by mistake).
• Push failed (you can push manually later) on member registration is expected without write access. Local config is still saved; teamai pull still works.

Write access and stats (do not grant write to every contributor)

digest / dashboard read stats/, sessions/, and members/ from the team repo. Those files are written via git, so no write ⇒ not in team stats.

Giving every internet contributor write on the hub repo is not acceptable.

Document the split:

Who	Hub repo access	Required setup	In team digest
Contributors	read	init + pull	no
Collaborators (after a few PRs)	write, main protected	full, including reports	yes

Do not document an internal / TGit contributor path in this public guide.

Out of scope

• CLI behavior changes (including fork-aware teamai push).
• HTTP report/sync/ack so read-only users appear in digest.
• Sweeping leftover master wording in other files (providers.md, comments, skills).

Acceptance

• CONTRIBUTING never says to branch from master.
• A contributor can complete build → link → init hub repo → pull, and understands a failed member push as normal.
• git status after init does not imply committing TeamAI local files into teamai-cli.

Read .github/CONTRIBUTING.md and compare its branch instructions with the issue’s required build, link, init, and pull flow. Update that file only so it uses origin/main, explains public team-repo dogfooding, access limitations, and expected push failures. Verify the documented acceptance points, including a clean git status after initialization.