Reorganize docs, rewrite changelog and add existing-install guidance

[lozenge0]

Summary

This PR applies the six "worth doing" items from the repository review.

Changes

• Move the seven dated experiment reports to docs/reports/. Links in the living documents point to the new paths. The reports themselves only link to each other, so they are unchanged.
• Fold docs/PLAN.md and docs/PUBLISHING.md into docs/MAINTAINER.md. The maintainer guide now has sections for fixed decisions, layout, checks, repository settings, release process and ongoing maintenance.
• Rewrite CHANGELOG.md in Keep a Changelog form with Added, Changed, Fixed and Known limitations. Process notes are gone. The v0.1.0 tag waits until the app is visible in the public catalog.
• Keep the file inventory only in tests/test_publication.py. The release review no longer carries a copy, and the test that compared the two is removed.
• Replace sentence assertions in the tests with heading, link and token checks. Tests no longer break when a sentence is rephrased.
• Add an "Already installed?" section to the README that explains what an existing installation can do about the icon and the port default, and link to it from the configuration reference.

The two stale test-count lines that remain are inside dated review records in docs/VALIDATION.md and describe what passed on those dates.

Testing

• python3 -m unittest discover -s tests passes all 28 tests.
• The relative-link test covers every moved report.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Nrm65fBRmGmRBTW3PhyeMm