docs: add clean-baseline README on main

Establish the www.archline.hu clean-baseline repo. This root commit on main
documents the baseline definition (only our code, deployable) and the
reproducible per-commit reconstruction method used on the build branch.

Signed-off-by: LÁZÁR Imre <imre@illusion.hu>
Assisted-by: claude-code@claude-opus-4-8

README.md

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+# www.archline.hu — clean baseline (constituents + generator)
+
+This repo produces the **clean code baseline** of the www.archline.hu docroot
+(Cadline, Joomla 3.8.11, host `tanis.cadline.hu`) — the post-compromise, malware-free,
+faithful reproduction of the live server's source files. The baseline is the **input**
+to the operator's HIDS baseline-diff verifier (per-vhost known-good reference); the
+verification itself runs there, not here.
+
+## Model: constituents + a generator script (not a checked-out tree)
+
+A deployed Joomla docroot differs from any repo/source layout: extensions install their
+files across many docroot paths (`administrator/…`, `components/…`, `media/…`,
+`plugins/…`) via their manifest. So this repo stores the baseline **constituents** and a
+script **assembles** the deployed baseline:
+
+```
+./build-baseline.sh            # → out/  = the deployed CODE docroot (the baseline)
+```
+
+- `core/` — Joomla 3.8.11 official package (deployed form).
+- `packages/<slug>/` — upstream-obtainable extensions; the pristine package is
+  manifest-mapped to deployed paths by `lib/jmap.py`, then our legit delta
+  (`cadline.patch`) is applied — so git history shows exactly how we differ from upstream.
+- `deployed/<slug>/` — no-source extensions: vetted live files, placed directly.
+- `cadline/<slug>/` — Cadline own-code (+ submodules for the deployed-layout Cadline repos).
+- `overrides/` — Cadline core modifications as patches on vanilla.
+- Malware (`malware-iocs.md`) and runtime data are excluded; the result is code only.
+
+See [`RUNBOOK.md`](RUNBOOK.md) for the build recipe and module inventory,
+[`PROVENANCE.md`](PROVENANCE.md) for per-extension origins, and
+[`malware-iocs.md`](malware-iocs.md) for the excluded IOC set.
+
+## Authority
+
+The live docroot (RO mirror) is the source of truth — the goal is its faithful,
+malware-free reproduction. The earlier single-commit "monolith" baseline is an
+unvalidated helper only (it dropped extension manifests and clean core files and kept
+installer junk); it is not a target.
+
+## References
+
+- The archline.hu 2026 security audit and incident analysis (operator-held).
+- The baseline is consumed by the operator's per-vhost HIDS baseline-diff verifier.