Make docker-compose.yml enforce the api/enterprise-api binary swap

Closes the local/dev half of a gap named repeatedly across this
phase's docs: Helm already made api/enterprise-api mutually exclusive
(same enterprise.enabled flag that turns on RBAC/audit/SSO, both
rendering to the same Service name/port); docker-compose.yml let both
run side by side, with nothing actually pointing at enterprise-api by
default.

Mechanism: both services now carry a `profiles` entry (single-tenant /
enterprise), selected via COMPOSE_PROFILES -- a new checked-in .env
sets single-tenant as the zero-config default (unchanged behavior for
anyone who doesn't touch it), and `COMPOSE_PROFILES=enterprise docker
compose up` swaps to enterprise-api instead. Docker Compose profiles
are purely additive (no "profile X excludes service Y" primitive), so
true exclusivity comes from both being profile-gated with no shared
default profile, not from one excluding the other directly.

Mirrors Helm's same-Service-name trick so alerting's API_QUERY_URL and
web's VITE_API_BASE_URL need zero conditional logic either way:
enterprise-api now maps host port 8080 (was 8083, its own binary
default -- overridden via HTTP_LISTEN_ADDR) and carries a
`networks.default.aliases: [api]` entry, so whichever binary is
actually running answers on the same compose-network hostname and host
port. alerting's and web's depends_on for api/enterprise-api are now
`required: false` (Compose's supported "optional dependency" shape) --
without it, compose errors on the inactive one rather than just
skipping it, since depends_on doesn't otherwise know about profiles.

Verified for real in this environment via `docker compose config`
(renders and validates the merged YAML without needing a daemon):
confirmed api/enterprise-api never both appear in --services output
for either profile selection, confirmed enterprise-api's rendered
block has port 8080/alias "api"/HTTP_LISTEN_ADDR ":8080" when the
enterprise profile is active, and confirmed `docker compose run
enterprise-api ...`/`docker compose build enterprise-api` (used by
enterprise/README.md's and phase-4-runbook.md's provisioning steps)
still work regardless of the active profile -- explicit service
references bypass profile filtering, confirmed by the commands
reaching a daemon-connection permission error rather than a
profile-resolution error. Not verified: an actual `docker compose up`
against a real daemon, still unavailable in this environment.

Docs updated in lockstep -- CLAUDE.md, threat-model.md (including its
summary table), phase-4-runbook.md (new §10a, §8's provisioning
commands updated for the new port/profile), enterprise/README.md.

CLAUDE.md

@@ -190,14 +190,20 @@ the fix verified Docker-free (`chrunner_test.go`'s and
 `searchclient_test.go`'s `TestSearchRefusesMidProvisioningTenant`-shaped
 tests) — see `api/queryapi/tenant_isolation_gap_test.go` for the full
 accounting of all four probes, now all closed. The deployment-
-topology gap that briefly was the largest one is now closed for Helm:
-`deploy/helm/sentry/templates/api.yaml`/`enterprise-api.yaml` are
-mutually exclusive on the same `enterprise.enabled` flag that turns on
-RBAC/audit/SSO, rendering to the same Service name/port either way — a
-Helm-deployed cluster can't accidentally run the wrong one.
-`docker-compose.yml` still runs plain `api` unconditionally, though
-(local/dev parity with the Helm chart's enforcement is real remaining
-work). Per-resource dashboard grants (the RBAC matrix's "(own/granted)"
+topology gap that briefly was the largest one is now closed for both
+Helm and docker-compose: `deploy/helm/sentry/templates/api.yaml`/
+`enterprise-api.yaml` are mutually exclusive on the same
+`enterprise.enabled` flag that turns on RBAC/audit/SSO, rendering to the
+same Service name/port either way — a Helm-deployed cluster can't
+accidentally run the wrong one. `docker-compose.yml`'s `api`/
+`enterprise-api` services are now the same mutually-exclusive choice,
+gated behind `COMPOSE_PROFILES` (`.env` checks in `single-tenant` as the
+zero-config default) and sharing a host port/network-alias trick so
+`alerting`/`web` need no conditional logic either way — verified via
+`docker compose config` (renders/validates without a daemon, confirms
+the two never both appear for one profile selection), not an actual
+`docker compose up` in this environment. Per-resource dashboard grants
+(the RBAC matrix's "(own/granted)"
 qualifier) are now enforced too: `api/dashboards.PermissionStore` (core
 interface) implemented by `enterprise/internal/rbacstore.
 DashboardPermissions`, wired in only by `enterprise-api` — an Editor can