Refactor project structure for modularity

Move model and pipeline components into dedicated modules
Extract utilities from CLI into shared helpers
Update imports throughout codebase
Refactor project structure for modularity

Move model configuration and hardware selection into `models/` package
Extract pipeline steps into `pipeline/` package
Add utility helpers in `utils/` package
Update CLI imports and references

src/audio_summary/models/device.py

@@ -0,0 +1,32 @@
+"""Hardware detection and automatic model selection.
+
+Detects the amount of unified memory available on the Apple Silicon machine and
+picks the most capable model tier that fits (see ``config.TIERS``).
+"""
+
+import psutil
+
+from .config import TIERS, Tier
+
+
+def detect_ram_gb() -> float:
+    """Return the total unified memory in gibibytes."""
+    return psutil.virtual_memory().total / (1024**3)
+
+
+def select_tier(ram_gb: float) -> Tier:
+    """Select the highest tier whose RAM requirement fits ``ram_gb``.
+
+    Falls back to the smallest tier if the machine has less memory than any
+    declared threshold (the models simply run slower / may swap).
+    """
+    eligible = [tier for tier in TIERS if tier.min_ram_gb <= ram_gb]
+    if eligible:
+        return max(eligible, key=lambda tier: tier.min_ram_gb)
+    return min(TIERS, key=lambda tier: tier.min_ram_gb)
+
+
+def select_models() -> tuple[float, Tier]:
+    """Detect memory and return ``(ram_gb, selected_tier)``."""
+    ram_gb = detect_ram_gb()
+    return ram_gb, select_tier(ram_gb)