Wrong formula in `ETH for rebalance` calculation

The formula in the docs seems to have misplaced parentheses.

Current (incorrect):

ETH for rebalance = stETH Liability - (1 - Reserve Ratio * Total Value) / Reserve Ratio

Should be:

ETH for rebalance = (stETH Liability - (1 - Reserve Ratio) * Total Value) / Reserve Ratio

Derivation:

X  - ETH for rebalance
L  - stETH Liability
RR - Reserve Ratio
TV - Total Value

HF = (TV * (1 - RR)) / L
We want to deduct X from TV and L to return health factor to 100% (1)

L - X = (TV - X) * (1 - RR)
L - X = TV - X - TV * RR + RR * X
X = (L - TV * (1 - RR)) / RR

Which gives:

ETH for rebalance = (stETH Liability - Total Value * (1 - Reserve Ratio)) / Reserve Ratio

Example:
For stETH Liability = 90, Total Value = 99, Reserve Ratio = 0.1:

• Current formula → ETH for rebalance = 90 - (1 - 0.1 * 99) / 0.1 = 179
• Correct formula → ETH for rebalance = (90 - (1 - 0.1) * 99) / 0.1 = 9

The result 179 is incorrect, it would mean rebalancing more ETH than exists in the stVault (99), which makes no sense.
With the corrected formula, the rebalance amount is 9, and checking the health factor after rebalancing confirms it returns to exactly 1, as intended.

Open run-on-lido/stvaults/building-guides/basic-stvault.md around line 447 and compare the displayed formula with the derivation and example in this issue. Update the documentation so the parentheses match the stated calculation, then verify the example produces the intended rebalance amount and health factor.