docs: contributor on-ramp - templates, code of conduct, welcoming CONTRIBUTING (PROJ-950)

[TAJD]

Contributor on-ramp for PROJ-950 (part of the PROJ-936 growth epic).

Draft: Tom must review the CONTRIBUTING.md wording before this merges. It's written in Tom's voice ("me, Tom") and needs his sign-off.

What changed

• .github/ISSUE_TEMPLATE/: YAML issue forms for bug (bug label), feature (enhancement), and question (question). They only use labels that already exist in the repo. config.yml keeps blank issues enabled and links SECURITY.md and the docs site.
• .github/PULL_REQUEST_TEMPLATE.md: summary, issue or Projektor ref, verification, and a checklist taken from AGENTS.md "Before opening a PR" and ci.yml (lint, type-check, coverage tests, gen:docs no diff, REST/MCP parity, migration registration). It also warns contributors not to add the release label, because that label triggers release-tag.yml.
• CODE_OF_CONDUCT.md: Contributor Covenant 2.1, using the official text unmodified.
• CONTRIBUTING.md: rewritten to invite contributions. It covers ways to help, running locally (from the AGENTS.md "Dev workflow" section), picking an issue (good first issue, comment first), where conventions live, the full CI command list, and review expectations. It's honest that there is one maintainer without opening on it.

.github/CODEOWNERS is not touched. Please merge this after PROJ-915's CODEOWNERS PR.

Needs a decision before merge

• Code of conduct enforcement contact. CODE_OF_CONDUCT.md contains the placeholder [maintainer contact: add before merge]. Replace it with a real contact route; I didn't invent one.
• CONTRIBUTING.md wording (Tom's voice): check the tone, the "nudge after a week" line, and "I may push small fixes to your branch".

How it was verified

• pnpm lint: pass
• pnpm gen:docs: no diff
• pnpm --filter @projektor/docs build: pass
• All issue-form YAML parses (yaml.safe_load).
• The rest of the CI list isn't affected, because this PR only changes .github/ and two root markdown files.

🤖 Generated with Claude Code

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