docs(content): revamp sliding-window examples and purge empty appendix pages

apps/docs/content/(01-linear-structures)/sliding-window/index.mdx

@@ -48,18 +48,14 @@ The window size never changes. The main task is updating the window state effici
 
 
 ```python
-def fixed_window(nums, k):
-    window_sum = 0
-    best = float('-inf')
-
-    for right in range(len(nums)):
-        window_sum += nums[right]            # add the new element
-
-        if right >= k - 1:                   # window is full
-            best = max(best, window_sum)     # record answer
-            window_sum -= nums[right - k + 1]  # remove the oldest element
-
-    return best
+def sliding_window_fixed(input, window_size):
+    ans = window = input[0:window_size]
+    for right in range(window_size, len(input)):
+        left = right - window_size
+        remove input[left] from window
+        append input[right] to window
+        ans = optimal(ans, window)
+    return ans
 ```
 
 <Steps>
@@ -87,24 +83,43 @@ Here the window expands until invalid, then shrinks until valid again.
 
 </Frame>
 
+
+<Tabs inline>
+  <Tab title="Longest Window">
+
 ```python
-def flexible_window(nums, target):
+def sliding_window_flexible_longest(input):
+    initialize window, ans
     left = 0
-    window_sum = 0
-    best = 0
-
-    for right in range(len(nums)):
-        window_sum += nums[right]            # grow the window
-
-        while window_sum > target:           # window is invalid
-            window_sum -= nums[left]         # shrink from the left
+    for right in range(len(input)):
+        append input[right] to window
+        while invalid(window):        # update left until window is valid again
+            remove input[left] from window
             left += 1
+        ans = max(ans, window)        # window is guaranteed to be valid here
+    return ans
 
-        best = max(best, right - left + 1)   # window is valid, record answer
-
-    return best
 ```
 
+  </Tab>
+  <Tab title="Shortest Window">
+
+```python
+def sliding_window_flexible_shortest(input):
+    initialize window, ans
+    left = 0
+    for right in range(len(input)):
+        append input[right] to window
+        while valid(window):
+            ans = min(ans, window)      # window is guaranteed to be valid here
+            remove input[left] from window
+            left += 1
+    return ans
+```
+
+  </Tab>
+</Tabs>
+
 <Steps>
   <Step title="">
   Add `nums[right]` to the window.
@@ -119,26 +134,6 @@ def flexible_window(nums, target):
 
 ---
 
-For "shortest window" problems, swap the logic: use `while` for the *valid* case, record the answer inside the loop, then shrink.
-
-```python
-def shortest_valid_window(nums, target):
-    left = 0
-    window_sum = 0
-    best = float('inf')
-
-    for right in range(len(nums)):
-        window_sum += nums[right]
-
-        while window_sum >= target:          # window is valid
-            best = min(best, right - left + 1)   # record, then try to shrink
-            window_sum -= nums[left]
-            left += 1
-
-    return best if best != float('inf') else 0
-
-```
-
 ## 3. Frequency-tracking windows
 
 :::tip