Modernize interaction model, upgrade to C++20, and fix build

- Removed legacy edge-panning from all mouse modes.
- Implemented universal panning via Middle Mouse Button (MMB), Spacebar + Left Mouse Button (LMB), two-finger gestures, and smooth trackpad scrolling.
- Transitioned Connection and Area Selection tools to a click-to-click model.
- Improved Connection tool UX with Cyan ghost lines and Green snap points.
- Centralized room-relative direction snapping logic in `src/map/ExitDirection.cpp`.
- Upgraded project to C++20 standard.
- Fixed C++20 migration issues: restored `concepts.h`, made `Crtp` constructors public, and resolved `std::unordered_map` transparency in `emojis.cpp`.
- Fixed build error in `src/syntax/Value.h` related to incomplete types in `std::vector`.
- Integrated `TestUIState` unit tests.
- Applied project-wide code formatting.

Author: nschimme

src/syntax/Value.cpp

@@ -137,6 +137,26 @@ Vector::Base::const_iterator Vector::end() const
     return m_vector->end();
 }
 
+bool Vector::empty() const
+{
+    return m_vector->empty();
+}
+
+size_t Vector::size() const
+{
+    return m_vector->size();
+}
+
+const Value &Vector::at(size_t pos) const
+{
+    return m_vector->at(pos);
+}
+
+const Value &Vector::operator[](size_t pos) const
+{
+    return at(pos);
+}
+
 Vector getAnyVectorReversed(const Pair *const matched)
 {
     size_t len = 0;

src/syntax/Value.h

@@ -38,11 +38,11 @@ struct NODISCARD Vector final
     NODISCARD Base::const_iterator end() const;
 
 public:
-    NODISCARD bool empty() const { return m_vector->empty(); }
-    NODISCARD size_t size() const { return m_vector->size(); }
+    NODISCARD bool empty() const;
+    NODISCARD size_t size() const;
     // NOTE: at() throws if out of range.
-    const Value &at(size_t pos) const { return m_vector->at(pos); }
-    const Value &operator[](size_t pos) const { return at(pos); }
+    const Value &at(size_t pos) const;
+    const Value &operator[](size_t pos) const;
 
 public:
     friend std::ostream &operator<<(std::ostream &os, const Vector &v);