docs: humility pass - frame as exploration, not declaration

- Remove "IDE of 2026" and "Integrated Delegation Engine" claims
- Rename "Core Innovations" to "Ideas We're Exploring"
- Remove "Universal" from data plane and propulsion docs
- Add experimental status badges
- Frame concepts as discovery, invite others to explore

Closes gt-qvn7.5.2

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/propulsion-principle.md

@@ -1,11 +1,11 @@
-# The Universal Gas Town Propulsion Principle
+# The Propulsion Principle
 
-> **Status**: Canonical Theory-of-Operation Documentation
+> **Status**: Design document (experimental)
 > **See also**: [sling-design.md](sling-design.md) for implementation details
 
-## The One Rule
+## The Core Idea
 
-Gas Town runs on a single, universal rule:
+We're trying a simple rule for agent behavior:
 
 > **If you find something on your hook, YOU RUN IT.**