gantry: size chair seeds by cluster capacity

[Vaibhav Patel (vpatelsj)]

Derive the active chair target from DaemonSet.status.desiredNumberScheduled as ceil(capacity * chair_seed_percentage / 100), with a minimum of one and chair_seed_count as the maximum

It calculates:

$$ \text{target}=\min\left(50,\max\left(1,\left\lceil\frac{\text{capacity}\times10}{100}\right\rceil\right)\right) $$

Examples:

• 3 desired Gantry pods → 1 chair

• 20 pods → 2 chairs

• 100 pods → 10 chairs

• 500+ pods → 50 chairs

• ship a 10% default capped at 50, add namespaced DaemonSet get RBAC, preserve the eight-chair E2E topology, and update the chair design docs