chore: add Codex project context and agent guidance

.agents/skills/kst4contest-change/SKILL.md

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+---
+name: kst4contest-change
+description: Analyze or implement KST4Contest Java/JavaFX changes, bug fixes, refactorings, protocol handling, contest workflow behaviour, callsign/band logic, AirScout/logging/rotor/DXCluster integrations, threading and state management. Use current code as source of truth and follow the mandatory concept-and-question gate before edits.
+---
+
+# KST4Contest change workflow
+
+Read the relevant reference files before proposing a concept.
+
+## Phase 1: read-only analysis
+
+- Inspect the current code and tests.
+- Identify the current data flow and thread ownership.
+- Identify user-visible and protocol-visible behaviour.
+- Check relevant `docs/PROJECT_CONTEXT.md` sections when they exist.
+- Check whether the task overlaps a known invariant in the references.
+- Do not modify files.
+
+## Phase 2: report understanding in German
+
+Explain:
+
+- what Marc wants changed;
+- what must remain unchanged;
+- which components appear affected;
+- what evidence in the current code supports that understanding;
+- any conflict between current code and historical project context.
+
+Never resolve a conflict by guessing.
+
+## Phase 3: questions and final concept in German
+
+Before finalizing the concept:
+
+- identify all material implementation choices;
+- ask Marc questions that are not already answered by code, project instructions or prior confirmed decisions;
+- wait for answers when needed.
+
+Then present:
+
+- intended data/control flow;
+- exact behavioural changes;
+- compatibility impact;
+- thread/UI impact;
+- persistence impact;
+- test strategy;
+- likely documentation impact;
+- likely durable project-context impact;
+- related-project impact when relevant.
+
+Ask for explicit concept approval and wait before editing.
+
+## Phase 4: implementation
+
+After approval:
+
+- implement the smallest coherent change;
+- preserve unrelated behaviour;
+- keep comments/Javadoc in English;
+- add/update focused tests;
+- keep external protocol parsing defensive;
+- avoid hidden defaulting for unknown values.
+
+## Phase 5: verification and documentation impact
+
+Run focused checks, then appropriate broader checks.
+
+Because KST4Contest build configuration may ignore failures/findings, inspect summaries and reports rather than only command exit status.
+
+Then use `$software-project-context`:
+
+- do a low-cost documentation-impact classification;
+- inspect only likely affected manual/README/website sections;
+- update targeted documentation when clearly required by the approved implementation;
+- update `docs/PROJECT_CONTEXT.md` for significant durable technical decisions/state changes;
+- do not perform a full manual audit unless there is a specific trigger.
+
+## Phase 6: report
+
+Report in German:
+
+- files changed;
+- implementation summary;
+- tests/checks;
+- warnings/findings;
+- documentation-impact result;
+- documentation/context updates or why none were required;
+- related-project impact when relevant;
+- unresolved issues;
+- no Git publication action unless explicitly requested.