Docs: consolidate active planning and archive historical material

The planning package had grown to where a new agent could not tell what was
authoritative. Phase 0 execution prompts sat beside the specification; four
completed milestone reports sat beside the current one; and upstream AI-DnD's
own `plan/` build log and `docs/` project site still described a hosted,
scripted, multi-user product with accounts — every screenshot in it showed a
Scripts tab and a Sign up button, none of which has existed since M2.

`planning/archive/` now holds the history and says so in its own README:
`phase0/` for the research that chose AI-DnD, `milestone-reports/` for M1 and
M2, `decisions/` for ADR 008, the Phase-0-before-build gate Phase 0 satisfied.
`planning/reports/` holds only the current milestone's report, because that is
the one M4 planning has to read; it moves to the archive when M4's replaces it.

Deleted rather than archived: the Phase 0B execution prompts and the
handoff/status/summary documents, the Phase 0A discovery and triage reports,
upstream's `plan/` and `docs/` trees, and `frontend/README.md`, which was Vite's
template boilerplate. All of it is in Git history, and the two recommendation
reports carry every conclusion the deleted research reached.

Archived documents are kept verbatim. Paths written inside them point at where
those files were when the document was written, which is the point: an evidence
record that has been quietly edited is no longer evidence.

Active documentation is corrected where it pointed at the removed trees or
described removed capability as present. `DEVELOPMENT.md`'s "things M1 did not
touch" list had gone stale at M2 and claimed QuickJS scripting was still tested;
its test count was 604 against an actual 638. `README.md` loses the upstream CI
badge, which reported upstream's pipeline rather than this fork's, and a
reference to `backend/app/worldstate/engine.py`, a file that does not exist.
`planning/README.md` is rewritten as the documentation index.

New: `planning/PROJECT-SOURCES.md` and `planning/project-sources.txt`, the
manifest of what belongs in the ChatGPT project's Sources.

Source comments referring to the deleted trees are reworded; no behaviour
changes. 638 backend tests pass, frontend lints and builds, and a reference scan
over all 48 tracked Markdown files reports no unresolved path in active
documentation.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NCbwH7yLGKsj1rhXXzKSCu

DEVELOPMENT.md

@@ -208,7 +208,7 @@ visible from within.
 ## Tests
 
 ```bash
-cd backend && .venv/bin/python -m pytest tests/ -q     # 604 tests
+cd backend && .venv/bin/python -m pytest tests/ -q     # 638 tests
 cd frontend && npm run lint && npm run build
 ```
 
@@ -266,21 +266,24 @@ docker exec app python -c "import socket; socket.create_connection(('1.1.1.1',44
 # -> OSError: Network is unreachable, and story turns still work
 ```
 
-`planning/reports/M1-BASELINE-REPORT.md` records the run this procedure is
+`planning/archive/milestone-reports/M1-BASELINE-REPORT.md` records the run this procedure is
 taken from, including the packet captures.
 
-## Things inherited from upstream that M1 deliberately did not touch
+## Things still inherited from upstream
 
-These are M2's scope (`planning/BUILD-MILESTONES.md`), listed here so nobody
-reports them as new:
+M2 removed the hosted, cloud, account, analytics, Postgres/Render and QuickJS
+scripting surfaces outright — `PROVENANCE.md` lists exactly what went. What is
+left of upstream that a newcomer might report as a defect:
 
-- hosted/multi-user/account/demo-key code, analytics tables, Postgres and
-  Render deployment paths, and the OpenRouter default endpoint constant all
-  still exist in the tree. None of them is reachable from a default local run,
-  and none requires a cloud service.
-- `docs/*.html` is upstream's GitHub Pages project site and still links Google
-  Fonts. It is not served by the application and is not part of any build.
-- `.github/workflows/ci.yml` is upstream's GitHub Actions pipeline. This
+- **Inert legacy tables and columns.** Five tables and four columns M2 emptied
+  of meaning are still in the schema, unmapped, so an M1-era campaign database
+  opens unchanged. Nothing reads or writes them. A cleanup migration waits for
+  the schema to settle after M5 (`planning/BUILD-MILESTONES.md`).
+- **Dual-dialect migration code.** `backend/app/migrations.py` still carries
+  SQLite/Postgres branches from upstream, although Postgres support itself is
+  gone and SQLite is the only store. Same cleanup, same milestone.
+- **`.github/workflows/ci.yml`** is upstream's GitHub Actions pipeline. This
   repository lives on a self-hosted Gitea; the workflow is kept for provenance
   and is not what runs the tests here.
-- QuickJS campaign scripting is still present and still tested.
+- **No frontend tests.** `npm run lint && npm run build` is the whole frontend
+  check. A test runner is M8's job.