feat: Add capsule_reports migration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

go-backend/migrations/20260218120000_add_capsule_reports.sql

@@ -0,0 +1,22 @@
+-- Capsule report system: members voluntarily submit decrypted evidence when reporting
+-- encrypted entries. The server stores the plaintext sample provided by the reporter.
+
+CREATE TABLE IF NOT EXISTS capsule_reports (
+    id              UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
+    reporter_id     UUID        NOT NULL REFERENCES profiles(id) ON DELETE CASCADE,
+    capsule_id      UUID        NOT NULL REFERENCES groups(id) ON DELETE CASCADE,
+    entry_id        UUID        NOT NULL REFERENCES capsule_entries(id) ON DELETE CASCADE,
+    decrypted_sample TEXT,      -- plaintext voluntarily provided by the reporter as evidence
+    reason          TEXT        NOT NULL,
+    status          TEXT        NOT NULL DEFAULT 'pending'
+                                CHECK (status IN ('pending', 'reviewed', 'actioned', 'dismissed')),
+    created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at      TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Prevent duplicate reports from the same user for the same entry
+CREATE UNIQUE INDEX IF NOT EXISTS uq_capsule_reports_reporter_entry
+    ON capsule_reports (reporter_id, entry_id);
+
+CREATE INDEX IF NOT EXISTS idx_capsule_reports_status   ON capsule_reports (status);
+CREATE INDEX IF NOT EXISTS idx_capsule_reports_capsule  ON capsule_reports (capsule_id);