docs: D6-D9 — HEALTHCHECK, env regression test, new docs, archive spec

Add Docker HEALTHCHECK and mail-path /healthz liveness; env-doc regression
test; architecture.md and development.md; product.md and expanded security.md;
retire live specification.md to docs/archive/.

Co-Authored-By: Claude <claude-opus-5-thinking-high@noreply@anthropic.com>

docs/development.md

@@ -0,0 +1,130 @@
+# SelfPost — development
+
+**What this file is.** How to build, test, and ship changes. Current sprint
+state lives in [progress.md](progress.md) — read that first after `/clear`.
+
+Product boundaries: [product.md](product.md). As-built layout:
+[architecture.md](architecture.md).
+
+---
+
+## Repository layout
+
+- `cmd/panel` — panel HTTP server + milter + log-tailer
+- `cmd/selfpost-backup` — CLI backup (`docker exec … selfpost-backup`)
+- `internal/` — domain logic, store, web handlers, health checks
+- `build/` — Dockerfile, supervisord, Postfix/OpenDKIM wiring, entrypoint
+- `deploy/` — `docker-compose.yml`, proxy examples, `.env.example`
+- `test/e2e/` — **separate Go module**; container integration tests
+
+---
+
+## Local Go workflow
+
+Requires Go 1.26+ and `CGO_ENABLED=0` (pure Go SQLite).
+
+```sh
+make vet          # go vet ./...
+make test         # go test ./...
+make build        # bin/panel, bin/selfpost-backup (VERSION=dev by default)
+make build VERSION=1.0.0
+```
+
+Or directly:
+
+```sh
+go vet ./...
+go test ./...
+go build -trimpath -ldflags "-X codeberg.org/mix/selfpost/internal/buildinfo.Version=dev" -o bin/panel ./cmd/panel
+```
+
+**Env documentation regression:** `go test ./cmd/panel -run TestLoadConfig` —
+new `loadConfig` keys must appear in README env lists
+([cmd/panel/envdoc_test.go](../cmd/panel/envdoc_test.go)).
+
+---
+
+## End-to-end tests
+
+Hermetic container suite (plan C.4):
+
+```sh
+make e2e
+# equivalent: cd test/e2e && go test -v -timeout 20m ./...
+```
+
+Uses `deploy/docker-compose.yml` + `test/e2e/compose.override.yml` (high
+ports, test hostname, fake DNS zone, smtp-sink). Requires **Docker + Compose v2**
+on the machine running tests. Not included in `go test ./...` of the main module.
+
+CI (`release.yml`): matrix build → e2e per arch → push `ghcr.io` on tag
+`vX.Y.Z`.
+
+---
+
+## Dev server (full container)
+
+When unit tests are not enough — Postfix, OpenDKIM, supervisord, real SMTP:
+
+**Typical setup:** edit locally → sync tree to dev host → build/test there.
+
+Documented dev host: `selfpost.mixfed.ru` (Debian 12). Sync example from
+[progress.md](progress.md):
+
+```sh
+tar -czf - --exclude=.git . | ssh root@selfpost.mixfed.ru \
+  'rm -rf /root/selfpost-src && mkdir -p /root/selfpost-src && tar -xzf - -C /root/selfpost-src'
+```
+
+On the server (Go in `/usr/local/go/bin` if not in PATH):
+
+```sh
+cd /root/selfpost-src
+/usr/local/go/bin/go vet ./...
+/usr/local/go/bin/go test ./...
+docker build -f build/Dockerfile -t selfpost:dev --build-arg VERSION=dev .
+```
+
+Manual smoke on production-like host: panel at `https://selfpost.mixfed.ru`,
+real LE cert, live deliverability — not replaceable by e2e alone (no outbound
+25 on CI runners, no real PTR/reputation).
+
+---
+
+## Commit and changelog protocol
+
+From [progress.md](progress.md):
+
+1. Meaningful step → entry under `[Unreleased]` in [CHANGELOG.md](../CHANGELOG.md)
+   (Keep a Changelog format).
+2. Commit on `main` unless asked for a branch. **Do not commit unless the user
+   asks.**
+3. Before `/clear` at end of a phase: update `progress.md`, verify acceptance
+   criteria, CHANGELOG, final commit.
+
+Documentation changes that add/rename env vars, panel routes, or observable
+mail behaviour ship in the **same commit** as the code change.
+
+Release tagging and image push — only on explicit request.
+
+---
+
+## Agent rules (formerly spec §12)
+
+1. **No git commits** without explicit instruction in the prompt.
+2. After Go changes: `go build`, `go vet`; fix all issues. Run `go test` when
+   tests exist.
+3. Before calling a container task done: image builds and container starts.
+4. Iterate: minimal skeleton first, then features.
+5. Security requirements in [security.md](security.md) — implement with the feature,
+   not deferred.
+6. Do not implement out-of-scope items ([product.md](product.md)) or change
+   fixed assumptions without agreement.
+7. For large tasks: propose a plan before coding unless the user already approved
+   one.
+8. Check licence compatibility of new Go dependencies (permissive or
+   GPL-family for AGPL-3.0 project).
+
+Model routing (from progress): security/infra → Opus; UI/docs → Sonnet;
+trivial mechanics → Haiku. Pre-release security **review** (not authorship) →
+Fable.