docs: add CONTRIBUTING.md + CODE_OF_CONDUCT.md (Lumos PUBLIC-Hygiene)

[marcohost33-maker]

Summary

Adds CONTRIBUTING.md + CODE_OF_CONDUCT.md to Lumos — the only PUBLIC repo in Coworkerz, so community-health files matter.

CONTRIBUTING.md

• Explains scope (single-file constraint per ADR LUMOS-001, Anthropic-only, no backend)
• Welcome contributions: bug reports, security, docs, small UX, browser-compat
• Not in scope: multi-file refactors, provider switches, telemetry
• Submit-a-change flow: issue first → fork+branch → minimal diff → browser-tested
• Code style: 2-space, single quotes, comments only for non-obvious why
• Review timeline: bugs ~3 days, PRs ~7 days (personal-project expectation set)
• License: license-pending per ADR-019; contributors agree to re-license

CODE_OF_CONDUCT.md

• Contributor Covenant 2.1 (verbatim from contributor-covenant.org)
• Contact: marcohost33@gmail.com with "Lumos CoC" in subject

Notes

• Vero F-Backlog fix (Lumos PUBLIC-Hygiene)
• Welle 4 Self-Audit aufgedeckt: Lumos hatte keine Community-Files trotz PUBLIC

Test plan

• GitHub erkennt CONTRIBUTING.md im Insights → Community Standards
• GitHub erkennt CODE_OF_CONDUCT.md
• Links untereinander funktionieren

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