v0.3.0

The SPICE / NAIF release. Adds seven SPICE tools behind an optional
[spice] extra — kernel furnishing, SPK ephemeris state, frame
rotations, body parameters, and kernel-defined time conversions — backed
by NASA NAIF's CSPICE through spiceypy. The tools register only when
spiceypy is importable (pip install astrodynamics-mcp[spice]), so the
base install stays SPICE-free.

Added

• SPICE tools behind an optional [spice] extra — the kernel-management
  trio (spice_load_kernel, spice_list_kernels, spice_unload_kernel)
  plus four query tools: spice_state (SPK position / velocity with
  light-time), spice_frame_transform (FK / PCK / TF frame rotations),
  spice_body_parameters (PCK radii / GM / pole and prime-meridian
  constants), and spice_time_convert (ET / UTC / SCLK via LSK / SCLK
  kernels). The tools furnish kernels into a process-global pool and
  query whatever the pool holds; every CSPICE call is serialised onto one
  dedicated worker thread, and https loads route through a NAIF-host
  allowlist and the XDG kernel cache. The slots register identically on
  stdio and Streamable HTTP (#120, #121, #122, #123, #124, #125, #126).
• Eval-suite SPICE coverage plus a fourth runnable example session — a
  Mars-state query that furnishes NAIF kernels and reads an SPK state —
  shipping a markdown transcript and a Python script that drives the same
  sequence against an in-process MCP server and asserts numerical
  tolerance (#127).
• Documentation for the v0.3 surface: a SPICE-integration design page
  covering the kernel model, the NAIF furnish-from-URL allowlist, and the
  process-global pool's trust boundary; tool-reference entries for all
  seven tools; and the [spice] install line and tools table in the
  README (#120, #129).