chore: add contributor templates (PTC-25)

[karlimess]

Part of PTC-25. Adds the baseline contributor templates:

• Bug report and feature request issue forms (.github/ISSUE_TEMPLATE/)
• A PR template
• Issue chooser config that routes questions to Discussions
• Also adds a Contributing section to the README, PTC-51

One thing to flag for review: I set blank_issues_enabled: false in config.yml, so people have to use the bug/feature forms or head to Discussions — no freeform blank issues. It keeps the Issues tab clean and matches the engagement-first push. But it's a bit opinionated for where we are, and there's a case for leaving blank issues on so an early contributor with an odd report isn't blocked by the forms. Happy either way — flag it if you'd rather I flip it to true before merge.

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[gemini-code-assist]

Code Review

This pull request introduces GitHub issue templates for bug reports and feature requests, a configuration file for issue templates, and a pull request template to standardize contributions. The reviewer suggested keeping blank issues enabled in the configuration to reduce friction for early contributors who might want to submit issues that do not fit the structured templates.

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[db-tycoon-stephen]

Defer to 1.11 due to missed review deadline