docs: remove references to the source app and recording

Prepare for open-sourcing: scrub the prior-art attribution from the spec,
agent guide, and code comments so the project documents its own behavior.

- Reword RULES_FEATURE_SPEC.md to describe OpenAppLock's rules feature
  directly (drop the screen-recording source line and "as observed"/
  "not demoed"/"as shown" framing)
- Replace "the reference app/UI/style/defaults" comments and test names
  with direct descriptions of the behavior
- No behavior change; comments, docs, and @Test display names only

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

OpenAppLockTests/RuleModelTests.swift

@@ -12,7 +12,7 @@ import Testing
 @MainActor
 @Suite("BlockingRule model & persistence")
 struct RuleModelTests {
-    @Test("Defaults match the reference app's new-rule defaults")
+    @Test("Defaults match the documented new-rule defaults")
     func defaults() {
         let rule = BlockingRule(name: "In the Zone")
         #expect(rule.kind == .schedule)