feat(core): add Camera abstraction for viewport scrolling

- Add Camera class with modes: vertical, horizontal, omni, floating
- Refactor scroll.py and demo to use Camera abstraction
- Add vis_offset for horizontal scrolling support
- Add camera_x to EffectContext for effects
- Add pygame window resize handling
- Add HUD effect plugin for demo mode
- Add --demo flag to run demo mode
- Add tests for Camera and vis_offset

engine/effects/__init__.py

@@ -6,6 +6,7 @@ from engine.effects.legacy import (
     glitch_bar,
     next_headline,
     noise,
+    vis_offset,
     vis_trunc,
 )
 from engine.effects.performance import PerformanceMonitor, get_monitor, set_monitor
@@ -45,4 +46,5 @@ __all__ = [
     "noise",
     "next_headline",
     "vis_trunc",
+    "vis_offset",
 ]

engine/effects/legacy.py

@@ -82,6 +82,37 @@ def vis_trunc(s, w):
     return "".join(result)
 
 
+def vis_offset(s, offset):
+    """Offset string by skipping first offset visual characters, skipping ANSI escape codes."""
+    if offset <= 0:
+        return s
+    result = []
+    vw = 0
+    i = 0
+    skipping = True
+    while i < len(s):
+        if s[i] == "\033" and i + 1 < len(s) and s[i + 1] == "[":
+            j = i + 2
+            while j < len(s) and not s[j].isalpha():
+                j += 1
+            if skipping:
+                i = j + 1
+                continue
+            result.append(s[i : j + 1])
+            i = j + 1
+        else:
+            if skipping:
+                if vw >= offset:
+                    skipping = False
+                    result.append(s[i])
+                vw += 1
+                i += 1
+            else:
+                result.append(s[i])
+                i += 1
+    return "".join(result)
+
+
 def next_headline(pool, items, seen):
     """Pull the next unique headline from pool, refilling as needed."""
     while True:

engine/effects/types.py

@@ -29,10 +29,11 @@ class EffectContext:
     terminal_height: int
     scroll_cam: int
     ticker_height: int
-    mic_excess: float
-    grad_offset: float
-    frame_number: int
-    has_message: bool
+    camera_x: int = 0
+    mic_excess: float = 0.0
+    grad_offset: float = 0.0
+    frame_number: int = 0
+    has_message: bool = False
     items: list = field(default_factory=list)