feat(scheduling): node tags + service placement_tags affinity (#58)

Operator-set node labels (node_agents.tags) gate which nodes a service
may schedule onto: services.placement_tags requires every listed tag.
auto and spread filter eligible agents by tags; tags are re-evaluated
each reconcile so retagging a node re-spreads replicas. Pin + tags and
local + tags rejected; empty array clears the requirement.

Surfaces: --placement-tags on services create/update, nodes update
--tags, MCP args, OpenAPI, node-detail tag editor, service-detail
placement-tags input.

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Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/mcpserver/server.go

@@ -53,7 +53,7 @@ func init() {
 	// Services
 	register(spec{"containr_services_list", "List services in a project", "GET", "/projects/{project_id}/services", []string{"project_id"}, nil, false})
 	register(spec{"containr_services_get", "Get a service by id", "GET", "/services/{id}", []string{"id"}, nil, false})
-	register(spec{"containr_services_create", "Create a service in a project. Args: name (required), type, image, git_repo, git_branch, environment, port, domain, replicas, volumes = [{type: volume|bind, source, target, read_only}], builder = auto|railpack|nixpacks|dockerfile|static, cpu, memory, cpu_reserve, memory_reserve, static_build_cmd, static_dir, node_id (agent id | 'auto' = least-loaded online node; image services only — remote nodes can't run git builds), spread (bool — distribute replicas across every online schedulable node; mutually exclusive with a node pin).", "POST", "/projects/{project_id}/services", []string{"project_id"}, nil, false})
+	register(spec{"containr_services_create", "Create a service in a project. Args: name (required), type, image, git_repo, git_branch, environment, port, domain, replicas, volumes = [{type: volume|bind, source, target, read_only}], builder = auto|railpack|nixpacks|dockerfile|static, cpu, memory, cpu_reserve, memory_reserve, static_build_cmd, static_dir, node_id (agent id | 'auto' = least-loaded online node; image services only — remote nodes can't run git builds), spread (bool — distribute replicas across every online schedulable node; mutually exclusive with a node pin), placement_tags (string array — remote placement only onto nodes carrying every tag; re-resolved per reconcile, pin overrides).", "POST", "/projects/{project_id}/services", []string{"project_id"}, nil, false})
 	register(spec{"containr_services_delete", "Delete a service. Requires confirm:true.", "DELETE", "/services/{id}", []string{"id"}, nil, true})
 	register(spec{"containr_services_start", "Start a service", "POST", "/services/{id}/start", []string{"id"}, nil, false})
 	register(spec{"containr_services_stop", "Stop a service", "POST", "/services/{id}/stop", []string{"id"}, nil, false})
@@ -66,7 +66,7 @@ func init() {
 	register(spec{"containr_services_move", "Move a service to another project the caller owns. Args: id, project_id (required).", "POST", "/services/{id}/move", []string{"id"}, []string{"project_id"}, false})
 	register(spec{"containr_services_logs", "Get service runtime logs. Args: id, tail (default 100).", "GET", "/services/{id}/logs", []string{"id"}, nil, false})
 	register(spec{"containr_services_exec", "Run a one-off command in the service container (30s ceiling). Args: id, command (required).", "POST", "/services/{id}/exec", []string{"id"}, []string{"command"}, false})
-	register(spec{"containr_services_update", "Update a service. Args: id, name, image, command, domain, restart_policy, healthcheck_path, cpu, memory, replicas, port, volumes = [{type: volume|bind, source, target, read_only}] — volumes replaces the whole mount list; pass [] to clear. maintenance_mode (bool), basic_auth = [{username, password}] — replaces all creds; [] clears. builder = auto|railpack|nixpacks|dockerfile|static, cpu_reserve, memory_reserve, static_build_cmd, static_dir (empty string clears reserves/static fields). sleep_enabled (bool) + sleep_idle_minutes (1-1440) enable scale-to-zero on idle; a wake placeholder answers traffic while the service resumes. node_id pins placement to a node agent ('auto' = least-loaded, 'local' = run on the Containr host). spread (bool) distributes replicas across every online schedulable node; mutually exclusive with a pin — clear node_id to 'local' first if pinned.", "PUT", "/services/{id}", []string{"id"}, nil, false})
+	register(spec{"containr_services_update", "Update a service. Args: id, name, image, command, domain, restart_policy, healthcheck_path, cpu, memory, replicas, port, volumes = [{type: volume|bind, source, target, read_only}] — volumes replaces the whole mount list; pass [] to clear. maintenance_mode (bool), basic_auth = [{username, password}] — replaces all creds; [] clears. builder = auto|railpack|nixpacks|dockerfile|static, cpu_reserve, memory_reserve, static_build_cmd, static_dir (empty string clears reserves/static fields). sleep_enabled (bool) + sleep_idle_minutes (1-1440) enable scale-to-zero on idle; a wake placeholder answers traffic while the service resumes. node_id pins placement to a node agent ('auto' = least-loaded, 'local' = run on the Containr host). spread (bool) distributes replicas across every online schedulable node; mutually exclusive with a pin — clear node_id to 'local' first if pinned. placement_tags (string array; [] clears) restricts auto/spread placement to nodes carrying every tag; mutually exclusive with an explicit pin — clear the pin first.", "PUT", "/services/{id}", []string{"id"}, nil, false})
 
 	// Domains
 	register(spec{"containr_domains_list", "List domains attached to a service", "GET", "/services/{id}/domains", []string{"id"}, nil, false})
@@ -173,7 +173,7 @@ func init() {
 	register(spec{"containr_nodes_get", "Get a node agent (admin)", "GET", "/agents/{id}", []string{"id"}, nil, false})
 	register(spec{"containr_agent_tokens_issue", "Issue an agent onboarding token (admin). Args: label.", "POST", "/agent-tokens", nil, []string{"label"}, false})
 	register(spec{"containr_agent_tokens_list", "List agent onboarding tokens (admin)", "GET", "/agent-tokens", nil, nil, false})
-	register(spec{"containr_nodes_update", "Update a node agent (admin). Args: id; optional auto_prune, name.", "PUT", "/agents/{id}", []string{"id"}, []string{"auto_prune", "name"}, false})
+	register(spec{"containr_nodes_update", "Update a node agent (admin). Args: id; optional auto_prune, name, tags (string array — placement labels services can require via placement_tags; [] clears).", "PUT", "/agents/{id}", []string{"id"}, []string{"auto_prune", "name", "tags"}, false})
 	register(spec{"containr_nodes_cordon", "Cordon a node: blocks new pins and 'auto' placements; running replicas stay (admin). Args: id.", "POST", "/agents/{id}/cordon", []string{"id"}, nil, false})
 	register(spec{"containr_nodes_uncordon", "Re-open a node for placement (admin). Args: id.", "POST", "/agents/{id}/uncordon", []string{"id"}, nil, false})
 	register(spec{"containr_nodes_drain", "Drain a node: cordon + remove all service containers via the agent + unpin affected services so they redeploy locally. Requires the node online (admin). Args: id.", "POST", "/agents/{id}/drain", []string{"id"}, nil, true})