feat: add TBF (Ehlers Truncated BandPass Filter) + fix all 64 warnings

TBF indicator:
- Sealed class with RingBuffer, stackalloc scratch, O(Length) per bar
- 7 core files: Tbf.cs, Tbf.Quantower.cs, Tbf.md, tbf.pine, 3 test files
- 67 tests (48 lib + 19 Quantower) all passing
- Full integration: sidebar, indexes, docs, Python bridge, exports

AMFM fix:
- Added envBuf.Clear()/smaBuf.Clear() after stackalloc in Batch
  (SkipLocalsInit garbage values caused 8.97e+65 blowup)

Warning fixes (64 → 0):
- Amfm.cs: S125 commented code removed, 11× IDE0011 braces
- Pta.cs: 11× IDE0011 braces on if/else/for/foreach
- Pta.Tests.cs: 14× IDE0011, S1481 unused var, S2699 assertion, 2× MA0074
- Lpf.Quantower.Tests.cs: 2× MA0074 StringComparison

Build: 0 warnings, 0 errors, 20,048 tests passing

python/quantalib/filters.py

@@ -25,6 +25,7 @@ __all__ = [
     "roofing",
     "sgf",
     "spbf",
+    "tbf",
     "ssf2",
     "ssf3",
     "usf",
@@ -248,6 +249,19 @@ def spbf(close: object, shortPeriod: int = 40, longPeriod: int = 60, rmsPeriod:
     return _wrap(output, idx, f"SPBF_{shortPeriod}", "filters", offset)
 
 
+def tbf(close: object, period: int = 20, bandwidth: float = 0.1, length: int = 10, offset: int = 0, **kwargs) -> object:
+    """Ehlers Truncated Bandpass Filter."""
+    period = int(period)
+    bandwidth = float(bandwidth)
+    length = int(length)
+    offset = int(offset)
+    src, idx = _arr(close)
+    n = len(src)
+    output = _out(n)
+    _check(_lib.qtl_tbf(_ptr(src), _ptr(output), n, period, bandwidth, length))
+    return _wrap(output, idx, f"TBF_{period}", "filters", offset)
+
+
 def ssf2(close: object, period: int = 14, offset: int = 0, **kwargs) -> object:
     """Super Smoother (2-pole)."""
     period = int(kwargs.get("length", period))