feat(i2s-discovery): extract from monolith

Step 4 of i2s-skill-split refactor. First atomic sub-skill extracted
from klarheit-mit-idea2self monolith.

Contents:
- SKILL.md: routing-pattern entry, 5 numbered phases (orientation,
  vertiefung, widerspruchspruefung, bestaetigung, datei-bootstrap)
  with entry/exit criteria. Description scoped to discovery triggers
  with explicit anti-triggers naming sibling i2s-* skills.
- workflows/discovery.md: full 5-step interview (git mv from
  klarheit-mit-idea2self/workflows/discovery-idea.md, rename
  detection preserved).
- references/kommunikationsregeln.md: curated extract from
  plugin-shared (tonality, markers, control commands,
  discovery-specific dialog heuristics, export rule).
- references/idee-format.md: curated extract from
  plugin-shared/export-formate.md, idee_format block only.
- templates/idea2self-vorlage.md: full copy from plugin-shared
  (this Skill bootstraps the idea2self-file in Phase 5).

Tools: Read, Write, Edit, Glob, Grep, AskUserQuestion, WebFetch,
WebSearch, TodoRead, TodoWrite.

skills/i2s-discovery/templates/idea2self-vorlage.md

@@ -0,0 +1,68 @@
+# Idea2Self: [Kurztitel]
+
+_Erstellt am [Datum]. Letzte Aenderung: [Datum]._
+_Prozess: Discovery -> Problem-Statement -> Persona -> Recherche -> Experiment -> Prototyp -> Action-Plan_
+
+---
+
+## Idee
+
+**Kurztitel:** [3-5 Woerter]
+**Kern:** [1-2 Saetze]
+**Motivation:** [Warum diese Idee?]
+**Zielgruppe (erste Vermutung):** [Fuer wen?]
+**Problem (erste Vermutung):** [Welches Problem?]
+**Kontext:** [Hintergrund, Ressourcen, Zeitbudget]
+**Scope-Ausschluss:** [Was wird NICHT adressiert?]
+
+_Erstellt am [Datum] via Discovery-Interview_
+
+---
+
+## Problem-Statement
+
+_[Wird in Workflow 2 befuellt]_
+
+---
+
+## Persona
+
+_[Wird in Workflow 3 befuellt]_
+
+---
+
+## Recherche-Report
+
+_[Wird in Workflow 4 befuellt]_
+
+---
+
+## Experiment-Card
+
+_[Wird in Workflow 5 befuellt]_
+
+---
+
+## Prototyp-Konzept
+
+_[Wird in Workflow 6 befuellt]_
+
+---
+
+## Action-Plan
+
+_[Wird in Workflow 7 befuellt]_
+
+---
+
+## Offene Punkte
+
+_Geparkte Gedanken aus allen Workflows_
+
+---
+
+## Changelog
+
+| Datum | Aenderung | Workflow/Anlass |
+|-------|-----------|----------------|
+| [Datum] | Datei angelegt, ## Idee befuellt | Discovery-Interview |