Fix conflict discard and merge view copy commands

- add Discard actions for conflicted files and conflict groups
  - restore discarded conflicts from HEAD in both index and working tree
  - restrict regular discard actions to changed tracked files
  - preserve default editor commands when replacing an editor document
  - enable copying from the read-only merge-view side panels
  - cover conflict restoration and merge-side copying
  - document build parallelism and function-spacing conventions

.agent/rules/build-project.md

@@ -46,6 +46,8 @@ Run this **after** all edits and **before** attempting to compile.
 ## Step 2: Compile the Project
 To compile the project in debug mode, execute the `make` command, ensuring you point to the correct directory for your current Operating System.
 
+### Build Parallelism
+
 Always use all processors reported by the platform when selecting the parallel job count. On Linux
 and other systems with `nproc`, use `-j$(nproc)` exactly; do not substitute an arbitrary fixed value
 such as `-j4`. Use the platform-equivalent processor-count command where `nproc` is unavailable.

.agent/rules/project-introduction.md

@@ -43,6 +43,12 @@ declarations and unqualified eepp type names, such as `UISplitter`, over repeate
 qualified names such as `EE::UI::UISplitter`. Keep explicit qualification only where it is required
 to resolve ambiguity or avoid importing an unusually broad namespace into an unsuitable scope.
 
+## Function Spacing
+
+Always leave one blank line between consecutive function declarations in headers and between
+consecutive function definitions in implementation files. This is a project-wide stylistic
+constraint, including short inline functions.
+
 ## Control-Statement Braces
 
 Use braces around the body of an `if`, `else`, `for`, `while`, or similar control statement whenever