feat: org capacity policy admin surface

ADR-0022 / Spec.System.Capacity pins layered capacity limits: a platform
ceiling per dimension is unbreakable, and each organization may only set a
lower `organizationLimit`. The effective limit is the minimum of the two
(`LayeredLimit.effective`); dimensions with no org override fall back to
the platform ceiling. No dimension may be unlimited (a ceiling must exist
before an org limit can be set, `LayeredLimit.Valid`).

Add the backend: the pinned 23 CapacityDimension set + labels
(src/capacity/dimensions.ts), platform ceilings sourced from existing
runtime env vars plus `HUB_CEILING_<DIMENSION>` (src/capacity/ceilings.ts),
the OrganizationCapacityPolicy prisma model + migration, the
getCapacityPolicy/setCapacityPolicy service enforcing LayeredLimit.Valid,
and org-admin GET/PUT /api/org/:orgSlug/capacity-policy routes wired into
the org route tree.

Add the admin-web surface: CapacityDimension/CapacityPolicyView api client
types, capacityPolicy/setCapacityPolicy methods, a `容量` nav entry, and a
capacity page that lists every dimension with its platform ceiling (or
`未配置` when unset), an org-limit input (disabled until a ceiling exists),
and a live effective-value column. Saving sends the partial limits map;
the service rejects values above the ceiling or for unconfigured dimensions.

hub/admin-web/src/routes/+layout.svelte

@@ -23,6 +23,7 @@
 		{ key: 'members', label: '成员', icon: 'members' as const },
 		{ key: 'teams', label: '团队', icon: 'teams' as const },
 		{ key: 'projects', label: '项目', icon: 'projects' as const },
+		{ key: 'capacity', label: '容量', icon: 'overview' as const },
 		{ key: 'provider', label: '供应方', icon: 'provider' as const },
 		{ key: 'feishu', label: '飞书', icon: 'feishu' as const },
 	];