docs: ratify vision revision across README/ARCHITECTURE/PORT_PLAN + ADRs 0002-0006

Folds the 2026-06-26 vision-revision pressure-test into the canonical
docs. The spec moves from Proposed to Ratified; the decisions it produced
land in the docs it said it would amend, with ADRs recording each
load-bearing reversal.

- README.md: reframe north star (AI-era contact-center engine, not
  Asterisk successor); persona; revised pillars (add data-ownership,
  demote WASM, promote spend-control); update 'what it is/isn't'.
- ARCHITECTURE.md: replace three-plane framing with fused per-call
  vertical + composable horizontal platform; remove control<->media
  hot-path gRPC hop; make the agent tap the central interface; add
  DX spine + GUI-as-API-client + k8s declarative/operational model.
  Also: 'too slow to police' -> 'too slow to enforce' (terminology).
- PORT_PLAN.md: recharacterize as capability checklist (not template);
  graduate contact-center capabilities to first-class domain; Rust-native
  trunk SIP rows; WASM demoted; thin-slice + capability ladder phasing.
- ADR-0001: marked Superseded by ADR-0003.
- ADR-0002 (new): north star + fused per-call core.
- ADR-0003 (new): Rust-native trunk SIP, no SBC shield.
- ADR-0004 (new): GPL-3.0-or-later license.
- ADR-0005 (new): Valkey as event bus + state store.
- ADR-0006 (new): WebRTC-first ingress; SIP endpoint deferred.
- vision-revision spec: status -> Ratified 2026-06-26.

docs/adr/0004-license.md

@@ -0,0 +1,48 @@
+# ADR-0004 — License: GPL-3.0-or-later
+
+- **Status:** Accepted
+- **Date:** 2026-06
+- **Closes:** the license open-decision carried in the founding docs
+
+## Context
+
+The founding docs (and the [vision-revision](../superpowers/specs/2026-06-26-vision-revision-design.md)
+open-decisions list) left license open. rutster is a self-hosted engine whose competitor set
+([ADR-0002](0002-north-star-and-fused-core.md)) includes cloud CCaaS that could *wrap-and-resell*
+it as a managed service — the classic strong-copyleft concern.
+
+## Decision
+
+**GPL-3.0-or-later.**
+
+Strong copyleft (requires source-sharing on binary conveyance), OSI-clean, modernized one notch
+over Asterisk's GPLv2+. `SPDX-License-Identifier: GPL-3.0-or-later`.
+
+## Alternatives considered
+
+- **AGPL-3.0-or-later** — *considered.* AGPL additionally closes the network-use / SaaS loophole:
+  GPLv3 §13 states network use is **not** conveyance (so a hosted service triggers no
+  source-sharing obligation); AGPL §13 fixes that, compelling source disclosure for network-served
+  use. Given that cloud CCaaS is a named competitor, AGPL would harder-prevent a vendor from
+  hosting rutster-as-managed-CCaaS without contributing back.
+- **GPL-3.0-or-later was chosen** in favor of simplicity and lower downstream-embedding friction
+  (operators and tooling/library authors integrating rutster avoid AGPL's network-trigger), while
+  remaining strong copyleft against proprietary forking of the engine itself.
+
+## Trade-off accepted deliberately
+
+A cloud competitor *can* host GPL rutster and owe source only on binary distribution, which for a
+hosted service may be nothing. The license is the **floor**, not the moat: the wedge — self-host
++ data-ownership + one auditable boundary + operational simplicity + data-ownership as a buying
+criterion — is the actual reason operators self-host rather than wrap.
+
+If cloud-wrap becomes a demonstrated threat, **re-evaluate AGPL-3.0-or-later** (this ADR's
+"or-later" clause permits that transition cleanly, since GPL-3.0-or-later is a strict subset of
+AGPL-3.0-or-later for recipients).
+
+## Consequences
+
+- **Positive:** OSI-clean strong copyleft in the Asterisk lineage; compatible with the project's
+  dependencies (Valkey BSD-3-Clause per [ADR-0005](0005-event-bus.md); Rust-ecosystem MIT/Apache crates).
+- **Negative:** the network-use loophole is open **by design choice** — mitigated by the wedge, not
+  the license.