docs(functions): standardize all function doc blocks to UNIX man-page style

Replace all ad-hoc inline comments between license headers and function
declarations with consistent SYNOPSIS / DESCRIPTION / ARGUMENTS / RETURNS /
EXAMPLE blocks across all 99 project-owned functions/ files. No executable
logic, variable names, or exit codes were modified.

Completes Task #6 from AGENTS.md (Retroactive Function Documentation
Standardization).

functions/__fzf_inline_picker.fish

@@ -7,15 +7,13 @@
 # DESCRIPTION
 #   Opens an interactive fzf session and injects the selected item directly
 #   into the command line at the cursor position. Bound to @@ by default.
-#   Requires fzf to be installed. Repaints the prompt after insertion.
+#   Repaints the prompt after selection or cancellation.
 #
 # RETURNS
-#   0  A selection was made and inserted into the command line
-#   0  No selection was made (fzf cancelled); command line is unchanged
+#   0  Always; no-op if fzf is cancelled
 #
 # EXAMPLE
-#   # Press @@ at the prompt — fzf opens, pick an item, it appears at cursor
-#
+#   # Press @@ at the command prompt to open fzf and insert the selected item.
 function __fzf_inline_picker
     # Open fzf and capture selection
     set -l selection (fzf)