feat: add Postgres store with append-only schema and migrations

internal/store connects via pgx and runs golang-migrate migrations
embedded in the binary (go:embed), so Deklarix stays a single binary
despite the move to Postgres. Schema covers the five MVP tables
(submission, asset, extraction, finding, evidence_package, participant).

extraction, finding and evidence_package are append-only by design: a
Postgres trigger rejects UPDATE/DELETE outright, since a corrigible
evidence archive isn't an evidence archive. Corrections to a finding are
new rows whose supersedes column points at the row they replace (set at
INSERT time on the new row, since the trigger blocks UPDATE on the old
one) — "currently valid" findings are the ones no other row supersedes.

scripts/test.sh now spins up a disposable Postgres container so the
store's integration tests (including the append-only guarantee) actually
run on every test.sh/release.sh invocation instead of silently skipping
for lack of DATABASE_URL.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/store/migrations/0001_init.down.sql

@@ -0,0 +1,11 @@
+DROP TRIGGER IF EXISTS evidence_package_append_only ON evidence_package;
+DROP TRIGGER IF EXISTS finding_append_only ON finding;
+DROP TRIGGER IF EXISTS extraction_append_only ON extraction;
+DROP FUNCTION IF EXISTS forbid_update_delete();
+
+DROP TABLE IF EXISTS participant;
+DROP TABLE IF EXISTS evidence_package;
+DROP TABLE IF EXISTS finding;
+DROP TABLE IF EXISTS extraction;
+DROP TABLE IF EXISTS asset;
+DROP TABLE IF EXISTS submission;

internal/store/migrations/0001_init.up.sql

@@ -0,0 +1,89 @@
+CREATE EXTENSION IF NOT EXISTS pgcrypto;
+
+CREATE TABLE submission (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    platform TEXT NOT NULL CHECK (platform IN ('instagram', 'tiktok', 'youtube', 'linkedin')),
+    post_type TEXT NOT NULL,
+    status TEXT NOT NULL DEFAULT 'draft' CHECK (status IN ('draft', 'checked', 'published', 'archived')),
+    caption TEXT,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE TABLE asset (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    submission_id UUID NOT NULL REFERENCES submission (id),
+    kind TEXT NOT NULL CHECK (kind IN ('image', 'video', 'file')),
+    path TEXT NOT NULL,
+    sha256 TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+-- Stufe 1: striktes JSON aus der Claude-Extraktion. Append-only, siehe Trigger unten.
+CREATE TABLE extraction (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    submission_id UUID NOT NULL REFERENCES submission (id),
+    payload JSONB NOT NULL,
+    model_version TEXT NOT NULL,
+    prompt_version TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+-- Stufe 2: Ergebnis pro Regel. Append-only, Korrektur = neue Zeile.
+-- supersedes zeigt auf die alte Zeile, die diese Zeile ersetzt (gesetzt
+-- beim INSERT der Korrektur, nie per UPDATE — der Trigger würde das
+-- verbieten). "Aktuell gültig" = Zeilen, auf die kein supersedes zeigt,
+-- siehe Index unten für den Anti-Join.
+CREATE TABLE finding (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    submission_id UUID NOT NULL REFERENCES submission (id),
+    extraction_id UUID REFERENCES extraction (id),
+    rule_id TEXT NOT NULL,
+    rule_version INTEGER NOT NULL,
+    severity TEXT NOT NULL CHECK (severity IN ('niedrig', 'mittel', 'hoch')),
+    message TEXT NOT NULL,
+    supersedes UUID REFERENCES finding (id),
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX finding_supersedes_idx ON finding (supersedes) WHERE supersedes IS NOT NULL;
+
+-- Dossier + Beweiskette (Hash, RFC-3161-Token). Append-only.
+CREATE TABLE evidence_package (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    submission_id UUID NOT NULL REFERENCES submission (id),
+    dossier_path TEXT NOT NULL,
+    sha256 TEXT NOT NULL,
+    timestamp_token BYTEA NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE TABLE participant (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    submission_id UUID NOT NULL REFERENCES submission (id),
+    role TEXT NOT NULL CHECK (role IN ('creator', 'agentur', 'marke', 'kanzlei')),
+    name TEXT NOT NULL,
+    vorgegeben BOOLEAN NOT NULL DEFAULT false,
+    freigegeben BOOLEAN NOT NULL DEFAULT false,
+    approved_at TIMESTAMPTZ,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+-- Ein Beweisarchiv, in dem man Zeilen ändern kann, ist kein Beweisarchiv.
+CREATE FUNCTION forbid_update_delete() RETURNS TRIGGER AS $$
+BEGIN
+    RAISE EXCEPTION 'append-only table: % on % is not allowed', TG_OP, TG_TABLE_NAME;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER extraction_append_only
+    BEFORE UPDATE OR DELETE ON extraction
+    FOR EACH ROW EXECUTE FUNCTION forbid_update_delete();
+
+CREATE TRIGGER finding_append_only
+    BEFORE UPDATE OR DELETE ON finding
+    FOR EACH ROW EXECUTE FUNCTION forbid_update_delete();
+
+CREATE TRIGGER evidence_package_append_only
+    BEFORE UPDATE OR DELETE ON evidence_package
+    FOR EACH ROW EXECUTE FUNCTION forbid_update_delete();