docs: add CONTRIBUTING, code of conduct, and Forgejo templates

Contributor onboarding for the self-hosted toolchain (issue #37):

- `CONTRIBUTING.md`: prerequisites, the bootstrap one-liner, the dev loop
  (`bin/x reseed` -> `bin/x bootstrap-cfree` -> `bin/x test`), stdlib-addition
  guidance, and the code/commit conventions (Conventional Commits, ludic-fmt,
  one-job-per-file, Ludic-not-C/Python/JS for new tooling).
- `.forgejo/issue_template/`: bug, proposal, and cleanup/DX templates.
- `.forgejo/pull_request_template.md`: a checklist covering tests, the
  bootstrap fixpoint, formatting, docs/inventory, and commit style.
- `.forgejo/CODEOWNERS` and a short `CODE_OF_CONDUCT.md`.

Closes #37

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.forgejo/CODEOWNERS

@@ -0,0 +1,4 @@
+# Default owner for everything in the repo. Forgejo requests review from these
+# owners on matching pull requests. See:
+# https://forgejo.org/docs/latest/user/code-owners/
+*       @orkun

.forgejo/issue_template/bug.md

@@ -0,0 +1,34 @@
+---
+name: "Bug report"
+about: "Something in the compiler, runtime, or tooling behaves incorrectly"
+title: "bug: "
+labels:
+  - bug
+---
+
+## What happened
+
+<!-- A clear description of the incorrect behaviour. -->
+
+## Minimal reproduction
+
+<!-- The smallest .ludic program (or command) that triggers it. -->
+
+```ludic
+```
+
+## Expected vs actual
+
+- **Expected:**
+- **Actual:**
+
+## Environment
+
+- Command used (e.g. `bin/x app foo.ludic --headless`):
+- Target (native macOS / headless / web-wasm):
+- Commit (`git rev-parse --short HEAD`):
+- OS / arch:
+
+## Notes
+
+<!-- Stack traces, generated IR, or anything else that helps. -->

.forgejo/issue_template/cleanup.md

@@ -0,0 +1,21 @@
+---
+name: "Cleanup / DX"
+about: "Repo hygiene, tooling, docs, or developer-experience improvements"
+title: ""
+labels:
+  - cleanup
+  - dx
+---
+
+## Problem
+
+<!-- What friction or inconsistency exists today? -->
+
+## Proposal
+
+<!-- What to change. Keep it scoped and low-risk. -->
+
+## Acceptance criteria
+
+- [ ]
+- [ ]

.forgejo/issue_template/proposal.md

@@ -0,0 +1,31 @@
+---
+name: "Proposal"
+about: "Propose new language, stdlib, or runtime surface"
+title: "Proposal: "
+labels:
+  - proposal
+---
+
+## Summary
+
+<!-- One or two sentences: what should exist that doesn't today. -->
+
+## Motivation
+
+<!-- What can't be done cleanly now? Who needs this and why? -->
+
+## Proposed surface
+
+<!-- The namespace/API or syntax you propose. Show it in use. -->
+
+```ludic
+```
+
+## Determinism & backends
+
+<!-- Ludic's runtime is deterministic fixed-point. Does this proposal stay
+     replay-safe? Does it work on native AND web-wasm, or is it host-gated? -->
+
+## Alternatives considered
+
+## Open questions

.forgejo/pull_request_template.md

@@ -0,0 +1,24 @@
+<!-- Thanks for contributing to Ludic! Please fill in the checklist below. -->
+
+## What & why
+
+<!-- What does this change and why? Link the issue: Closes #NN -->
+
+Closes #
+
+## Checklist
+
+- [ ] `bin/x test` passes.
+- [ ] For compiler/runtime changes: `bin/x reseed && bin/x bootstrap-cfree`
+      still reaches the self-hosting fixpoint with no C compiler in the loop.
+- [ ] `ludic-fmt` leaves the touched files unchanged (2-space, LF, UTF-8).
+- [ ] New/changed stdlib symbols are documented under `docs/language/**` and
+      registered in `tools/docgen/inventory.json`
+      (`python3 tools/docgen/check.py` passes).
+- [ ] Commits follow [Conventional Commits](https://www.conventionalcommits.org).
+- [ ] No new C / Python / JS in tooling (Ludic only), and no generated
+      artifacts committed outside `build/` / `bin/`.
+
+## Notes for reviewers
+
+<!-- Anything reviewers should look at closely, or follow-ups deferred. -->