Add algorithm problems 9–11 to web3Task1 Go solution set

[Copilot]

The repository contained solutions for 8 classic algorithm problems but lacked a Go module definition, preventing the project from building as a proper module. Three additional problems have been added following the established pattern.

Changes

• go.mod: Initializes the project as a proper Go module (web3task1)
• 题目9 – Climbing Stairs (climbStairs): O(n) time, O(1) space DP solution (Fibonacci variant)
• 题目10 – Maximum Subarray (maxSubArray): Kadane's algorithm returning the maximum contiguous subarray sum
• 题目11 – Reverse Linked List (reverseList): Iterative in-place reversal with a new ListNode type definition

// Example outputs
climbStairs(10)                                    // → 89
maxSubArray([]int{-2, 1, -3, 4, -1, 2, 1, -5, 4}) // → 6  ([4,-1,2,1])
reverseList(1→2→3→4→5)                             // → 5→4→3→2→1

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