Add CORS credentials, transactional endpoints, and container deployment

CORS
  cors.go never set Access-Control-Allow-Credentials, so the
  cookie-authenticated API was unreadable from any cross-origin frontend:
  the server answered correctly and the browser blocked the page from
  reading it. Set for allowlisted origins on both the preflight and the
  actual response. Three tests added.

  HTTP_COOKIE_SAMESITE (lax|none|strict, default lax) is new. CORS is only
  half of what a cross-origin browser call needs; SameSite is judged on
  registrable domain, so a frontend on an unrelated domain gets perfect CORS
  headers and still no cookie. "none" is the only value that survives that,
  and validate() refuses it without the Secure flag.

  The "*" rejection now explains itself: browsers refuse Allow-Origin "*"
  together with credentials, so it would break every authenticated call
  rather than loosen anything.

Transactional endpoints (api-contract.md 12.1)
  POST /api/v1/job-applications/{id}/hire
  POST /api/v1/job-postings/{id}/assignments

  Replaces two client-side loops that wrote several records with no
  transaction and no rollback. Each is now one endpoint and one transaction,
  built over repo.Repo so org scoping, derived columns, type casts and error
  translation are not re-derived. Authorization reuses the existing policy
  table rather than adding a parallel one: a workflow is exactly as
  privileged as the writes it performs. 13 tests, including both rollback
  paths.

Bug fix in the repository layer
  repo.bindValue handled int64/int/float64/string but not int32, which is
  what pgx returns for a PostgreSQL `int` column. Nothing previously read a
  record and wrote one of its fields elsewhere, so it never surfaced; the
  hire flow does exactly that and failed with "ai_score must be a number".
  Both KindInt and KindFloat now accept the widths pgx actually produces.

Deployment
  infrastructure/Dockerfile.api  multi-stage, cross-compiling (BUILDPLATFORM
    + GOARCH) so linux/amd64 builds from arm64 are compiled rather than
    emulated. Alpine runtime, non-root uid 10001, 22.1 MB. Ships api, seed,
    setpassword and migrate, plus the migrations, so a Kubernetes
    initContainer can apply the schema from the same image and tag as the
    API. HEALTHCHECK keys on status code, not body, so a "degraded" instance
    is not pulled from rotation during a migration window.

  infrastructure/docker-compose.yml  migrations run to completion before the
    API starts. Assumes a managed PostgreSQL; the local-db overlay adds one
    with TLS enabled so APP_ENV=production is met rather than dodged.

  scripts/drop_public_tables.go  the one-off used to clear an unrelated
    schema from krowdb on 2026-08-24, kept for the record. Build-tagged
    ignore and gated on CONFIRM_DROP=yes.

Verified against PostgreSQL: 16/16 new tests pass, and the image was built,
run and exercised end to end (login, CORS preflight, authenticated reads,
transaction rollback).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CmQiGq73Uyfq7J4yR8Vxxw

Makefile

@@ -135,3 +135,57 @@ migrate-force: ## Clear a dirty state: make migrate-force VERSION=1
 .PHONY: verify-schema
 verify-schema: ## Print the tables, enums, FKs and indexes that exist in the target schema
 	@$(PSQL) -f scripts/verify_schema.sql
+
+# ── Docker ──────────────────────────────────────────────────────────────────
+#
+# These read infrastructure/.env, NOT the repository-root .env that `make run`
+# uses. Two files on purpose: the root one points at a developer's database
+# from the host, the infrastructure one points at a deployment's database from
+# inside a container, and DATABASE_HOST is different in each.
+
+COMPOSE_DIR   := infrastructure
+COMPOSE_FILES := -f docker-compose.yml
+# Layer the local database in with: make docker-up LOCAL_DB=1
+ifdef LOCAL_DB
+COMPOSE_FILES += -f docker-compose.local-db.yml
+endif
+COMPOSE = cd $(COMPOSE_DIR) && docker compose $(COMPOSE_FILES)
+
+.PHONY: docker-build
+docker-build: ## Build the API image
+	$(COMPOSE) build
+
+.PHONY: docker-up
+docker-up: ## Start the stack (migrations run first). LOCAL_DB=1 adds PostgreSQL
+	$(COMPOSE) up -d --build
+	@echo "api:    http://127.0.0.1:8080/health"
+	@echo "logs:   make docker-logs"
+
+.PHONY: docker-down
+docker-down: ## Stop the stack, keeping volumes
+	$(COMPOSE) down
+
+.PHONY: docker-logs
+docker-logs: ## Follow the API logs
+	$(COMPOSE) logs -f api
+
+.PHONY: docker-ps
+docker-ps: ## Show stack status and health
+	$(COMPOSE) ps
+
+.PHONY: docker-migrate
+docker-migrate: ## Apply migrations only, without starting the API
+	$(COMPOSE) run --rm migrate
+
+.PHONY: docker-seed
+docker-seed: ## Load the demo fixture into the deployment's database
+	$(COMPOSE) run --rm --entrypoint /usr/local/bin/seed api
+
+.PHONY: docker-setpassword
+docker-setpassword: ## Set a password: make docker-setpassword EMAIL=demo@krow.app
+	@test -n "$(EMAIL)" || { echo "usage: make docker-setpassword EMAIL=demo@krow.app"; exit 1; }
+	$(COMPOSE) run --rm -it --entrypoint /usr/local/bin/setpassword api -email $(EMAIL)
+
+.PHONY: docker-config
+docker-config: ## Render the fully resolved compose configuration
+	$(COMPOSE) config