Correct the README to match what the project actually contains

[ialakey]

The README described a version of this project that no longer exists. This
brings it in line with what is actually in the repository — every statement in
it was checked against the code, the assets and the build files.

Removed — not in this project

• The "three-repository system" table. It presented a Spring Boot API as
  the source of locations, guides and the Telegram directory. The app makes no
  backend calls; all three are bundled assets (assets/data/). Verified by
  grep — there is no API client in lib/.
• Screenshots. They showed the pre-redesign UI: the navigation drawer and
  nested bottom bars that were replaced by a single NavigationBar. The image
  links still resolve, but they no longer show this app.
• The iOS platform badge. ios/ has no Podfile and declares
  IPHONEOS_DEPLOYMENT_TARGET = 11.0, below what the current plugin set
  requires. It is not built or released. Now recorded honestly under
  Platforms rather than advertised.
• Stale package references — flutter_markdown, share, and a
  "five parsers" count that predates the rewrite.

Corrected

• "It works with no connection." That was true when guide images were
  bundled. The synced guide references 283 images hosted on srb.guide, so the
  text is offline and the images are not. The README now says exactly that,
  including the placeholder fallback.
• Flutter/Android versions, article and section counts, and the parser count
  now match the build files and guide.json.

Added — present but undocumented

• Android toolchain versions (AGP 9.1, Gradle 9.3.1, Kotlin 2.4, Java 17,
  targetSdk 36, minSdk 24).
• The checklist and deadline-reminder features, including why reminder
  scheduling is deliberately inexact.
• The exact commands CI runs, so they can be reproduced locally.
• Why tool/validate_guide.dart and parsers.yml exist — both guard against
  silent failure, which is not obvious from the workflow files alone.

Docs only; no code changes.