docs: setup files and the client, shared and CI docs describe what is (#6277)

.dockerignore, .gitignore, deploy/initdb, ci-requirements.md,
client/README.md, shared/README.md and two web/scripts test names: dates,
issue/rule/spike ids and the stories behind each exclusion removed.

Corrected:
- client/README.md: the dev lane bundles its own APK; :main no longer
  exists; main bundles the recorded sidecar instead of re-deriving the
  version name. Its smoke-test step wrote a bare "v0.2.0", which the
  server rejects as a sidecar that is not JSON; it now writes the JSON
  shape, which the README documents.
- ci-requirements.md: one workflow, not four; the android lane builds no
  debug APK; main reads the recorded sidecar.
- .gitignore: CI fills client/ on every image build, not tag releases only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.dockerignore

@@ -9,12 +9,8 @@ web/build
 # The Android client — built by its own job, never from this context. The APK
 # reaches the image through client/, downloaded as a CI artifact, so nothing
 # here reads android/ sources.
-#
-# This block named `flutter_client/` until 2026-09-10 and lost its PATTERN when
-# that tree was deleted, leaving a comment describing an exclusion that was no
-# longer happening. android/ never took its place, so 4.1 MB of Gradle project
-# has been entering the context and busting the `COPY . .` layer on every
-# Android-only change.
+# Excluded so the Gradle project neither bloats the context nor busts the
+# `COPY . .` layer on every Android-only change.
 android/
 
 # Local `make build` output — an 18 MB binary the image never uses, since the