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/RuleConfigurationTests.swift

@@ -18,7 +18,7 @@ struct RuleConfigurationTests {
         #expect(RuleConfiguration.openLimit(OpenLimitConfig()).kind == .openLimit)
     }
 
-    @Test("Defaults match the reference app's new-rule defaults")
+    @Test("Defaults match the documented new-rule defaults")
     func defaults() {
         let schedule = RuleConfiguration.default(for: .schedule).scheduleConfig
         #expect(schedule?.startMinutes == 9 * 60)