chore: move four distros into Images, and bring the docs up to date

[oonid]

Keeps the container list focused on the distributions in use.

What changes

• The main list offers Alpine (latest and edge), Debian (stable and testing), Fedora and Ubuntu.
• Arch Linux, Manjaro, openSUSE and Rocky Linux move into the Images suggestions on the custom-image card. Arch was already there; Manjaro, openSUSE Tumbleweed and Rocky Linux are added with the same image references and aliases as before. One tap fills the image reference and alias.
• A container already installed under one of those aliases still shows in the list, because the list also includes installed containers that are not in the catalog.
• README's "Supported distributions" updated.

Docs brought up to date with #16 and #17

• README:
  • "What it does" covers the list plus Images, background sessions, list operations with Cancel, and the verified layer cache.
  • Testing lists all four suites with current counts: app JVM 128, pr-cli 178, instrumented 8, on-device 55. It notes that CI runs both unit suites.
  • Project structure and the Documentation table add the background-sessions design and the architecture doc; docs/plans/ is marked historical.
• docs/android-apk-architecture.md:
  • the file tree is corrected (ProotLauncher and PtyNative now live in proot-engine);
  • stale claims about Back, onDestroy, and install/remove running in a PTY are fixed;
  • the "APK not built yet" follow-up is marked resolved.
• docs/design/background-sessions.md: the "today" context is past tense, pr-cli is no longer listed as unchanged, and the host test count is 178.
• docs/integration-tests.md: Test and Remove are in a row's ⋮ menu.
• docs/plans/background-sessions-followups.md: a historical-plan note.
• AGENTS.md:
  • the pr-cli test breakdown (153 library, 11 binary, 14 integration) and the Test menu entry;
  • Testing now lists the app JVM suite and notes that the guest test binary must be built before cargo test.
• From the pre-merge review:
  • the README qualifies Cancel's cleanup: only installs with an alias are cleaned up;
  • CI is described as running on pushes to main and on pull requests;
  • the README says when the switch and the battery banner show;
  • the "session ended" notice applies to sessions that end on their own;
  • the README points to the 24/7 limits;
  • the command blocks are paste-safe;
  • the APK doc's file tree matches the current layout, under a note that the T4.x sections are the Phase 4 record.
• The long-running use case is described generically (an AI agent's gateway, with Hermes as one example) in the background-sessions design, the historical plan and one proot note.
• Dated test results, history and exploration docs are left as written.

Verification

• App unit tests: 128 passed (CI runs them along with cargo test).
• On the device:
  • the main list shows only the six entries, plus installed containers;
  • the Images popup lists the four after scrolling;
  • tapping Rocky Linux fills docker.io/library/rockylinux:latest with alias rockylinux.
• An installed container under a moved alias takes its title from the Images suggestions. On the device, a rockylinux container shows as "Rocky Linux" in the list.

Docs brought up to date with #16 and #17

• README:
  • "What it does" covers the list plus Images, background sessions, list operations with Cancel, and the verified layer cache.
  • Testing lists all four suites with current counts: app JVM 128, pr-cli 178, instrumented 8, on-device 55. It notes that CI runs both unit suites.
  • Project structure and the Documentation table add the background-sessions design and the architecture doc; docs/plans/ is marked historical.
• docs/android-apk-architecture.md:
  • the file tree is corrected (ProotLauncher and PtyNative now live in proot-engine);
  • stale claims about Back, onDestroy, and install/remove running in a PTY are fixed;
  • the "APK not built yet" follow-up is marked resolved.
• docs/design/background-sessions.md: the "today" context is past tense, pr-cli is no longer listed as unchanged, and the host test count is 178.
• docs/integration-tests.md: Test and Remove are in a row's ⋮ menu.
• docs/plans/background-sessions-followups.md: a historical-plan note.
• AGENTS.md:
  • the pr-cli test breakdown (153 library, 11 binary, 14 integration) and the Test menu entry;
  • Testing now lists the app JVM suite and notes that the guest test binary must be built before cargo test.
• From the pre-merge review:
  • the README qualifies Cancel's cleanup: only installs with an alias are cleaned up;
  • CI is described as running on pushes to main and on pull requests;
  • the README says when the switch and the battery banner show;
  • the "session ended" notice applies to sessions that end on their own;
  • the README points to the 24/7 limits;
  • the command blocks are paste-safe;
  • the APK doc's file tree matches the current layout, under a note that the T4.x sections are the Phase 4 record.
• The long-running use case is described generically (an AI agent's gateway, with Hermes as one example) in the background-sessions design, the historical plan and one proot note.
• Dated test results, history and exploration docs are left as written.

Verification

• Unit tests: 62 passed.
• On the device:
  • the main list shows only the six entries, plus installed containers;
  • the Images popup lists the four after scrolling;
  • tapping Rocky Linux fills docker.io/library/rockylinux:latest with alias rockylinux.