feat: add form response submition endpoint and forms filtering

internal/db/sqlc/migrations/000003_init_responses.up.sql

@@ -0,0 +1,22 @@
+BEGIN;
+
+CREATE TABLE form_responses (
+    id         UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
+    form_id    UUID        NOT NULL REFERENCES forms(id) ON DELETE RESTRICT,
+    user_id    UUID        REFERENCES users(id) ON DELETE SET NULL,
+    submitted_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE TABLE response_answers (
+    id          BIGSERIAL   PRIMARY KEY,
+    response_id UUID        NOT NULL REFERENCES form_responses(id) ON DELETE CASCADE,
+    question_id UUID        NOT NULL,
+    form_id     UUID        NOT NULL,
+    answer_text TEXT,
+    FOREIGN KEY (form_id, question_id) REFERENCES questions(form_id, id) ON DELETE CASCADE
+);
+
+CREATE INDEX idx_form_responses_form_id ON form_responses(form_id);
+CREATE INDEX idx_response_answers_response_id ON response_answers(response_id);
+
+COMMIT;