docs: add CONTRIBUTING.md, CODE_OF_CONDUCT.md, PR template

[MikeGatsby]

What this PR does

Adds the three required community-onboarding files this repo is currently
missing, per #54:

• CONTRIBUTING.md — setup, the exact pytest / ruff check src tests scripts commands, the 5 required CI checks, and the privacy/Contoso rule
  pulled from the README and docs/LAUNCH.md.
• CODE_OF_CONDUCT.md — Contributor Covenant 2.1, as requested in the issue.
• .github/PULL_REQUEST_TEMPLATE.md — the 4-item checklist from the issue's
  acceptance criteria (tests/ruff pass, no personal writing or paths,
  Contoso-safe docs/screenshots, linked issue).

Closes #54

Testing

• scripts/sanitize_check.sh passes locally (Sanitize OK (96 files)) —
  this is the CI check that applies to a docs-only change; no Python
  files were touched, so pytest / ruff have nothing new to exercise.
• Manually verified: a new contributor can go from clone to pytest
  using only CONTRIBUTING.md's Setup + Running checks sections.
• Privacy/Contoso rules stated up front in CONTRIBUTING.md, not buried.
• .github/PULL_REQUEST_TEMPLATE.md will appear on new PRs once merged
  (standard GitHub behavior for that path).

AI assistance disclosure

This PR was drafted with AI assistance (Claude, Anthropic) under human
review before submission. No repository policy on AI-assisted contributions
was found in CONTRIBUTING.md, AGENTS.md, README, or any PR template (none
existed prior to this PR) — disclosing regardless, per general good practice
around AI-assisted OSS contributions.

[telivity-otaip]

Hey @MikeGatsby — thank you for #63. The docs look solid and we’re giving you credit.

Why checks looked “missing” on your PR

1. GitHub parked the fork workflow as action_required (first-time contributor approval) — see run 31731194101. The workflow file exists; it just never got to run.
2. The repo ruleset requires a PR to merge but does not yet require the CI job names as status checks.

We couldn’t push onto your fork branch from here, so we opened a same-repo follow-up that:

• keeps your CONTRIBUTING / template work
• completes the Covenant 2.1 enforcement guidelines
• aligns CI with the documented ruff check src tests scripts
• attributes you via Co-authored-by: MikeGatsby <mikael.gatfi@gmail.com>

→ Follow-up PR: will link in a moment (branch cursor/issue-54-docs-and-ci-1b4f).

Once that one is green, please close this PR as superseded — you still get the contribution credit. Appreciate you kicking this off.

[telivity-otaip]

Follow-up with credit + CI fixes: #64

Please close this one as superseded once #64 is green — your Co-authored-by is on the commit.

[telivity-otaip]

Sorry @MikeGatsby — ignore the earlier "supersede" comments. We are not replacing this PR. We'll continue the work here on #63. Thank you again.

[telivity-otaip]

Pushed a small follow-up onto this branch (docs only): complete Covenant 2.1 enforcement guidelines, add sanitize to the local checklist, and note the first-time-contributor Actions approval.

Could not update .github/workflows/ci.yml from here (GitHub App cannot write workflow files on a fork). Existing CI is unchanged and will run once a maintainer clicks Approve and run workflows.