feat: add self-contained link composer

- Add structured URL codec with compact alphabets and dictionary support.
- Add public decode, redirect, and QR endpoints for composed links.
- Add authenticated encode API and link composer UI.
- Generate PNG QR codes via qrcode with Pillow support.
- Register the new blueprint and navigation entry.
- Cover public decode, auth gating, redirect URL parsing, and QR output.
- Bump NanoShare to 1.27.0 and lock new dependencies.

link_composer/bitstream.py

@@ -0,0 +1,48 @@
+class BitWriter:
+  def __init__(self) -> None:
+    self._bits: list[int] = []
+
+  @property
+  def bit_length(self) -> int:
+    return len(self._bits)
+
+  def write(self, value: int, width: int) -> None:
+    if width < 0:
+      raise ValueError("width must be positive")
+    if value < 0 or value >= (1 << width):
+      raise ValueError(f"value {value} does not fit in {width} bits")
+    for shift in range(width - 1, -1, -1):
+      self._bits.append((value >> shift) & 1)
+
+  def to_bytes(self) -> bytes:
+    padding = (-len(self._bits)) % 8
+    bits = self._bits + [0] * padding
+    out = bytearray()
+    for i in range(0, len(bits), 8):
+      byte = 0
+      for bit in bits[i : i + 8]:
+        byte = (byte << 1) | bit
+      out.append(byte)
+    return bytes(out)
+
+class BitReader:
+  def __init__(self, data: bytes, bit_length: int) -> None:
+    self._bits: list[int] = []
+    for byte in data:
+      for shift in range(7, -1, -1):
+        self._bits.append((byte >> shift) & 1)
+    self._bits = self._bits[:bit_length]
+    self._pos = 0
+
+  def read(self, width: int) -> int:
+    if self._pos + width > len(self._bits):
+      raise ValueError("payload ended unexpectedly")
+    value = 0
+    for bit in self._bits[self._pos : self._pos + width]:
+      value = (value << 1) | bit
+    self._pos += width
+    return value
+
+  @property
+  def remaining(self) -> int:
+    return len(self._bits) - self._pos