fix: v0.4.3 — inspect_image rendering polish (follow-up to #4)

Three live-NAS observations that the 0.4.2 implementation got wrong:

1. Header showed "?:?" — DSM Image/get returns image="" and tag=""
   for name:tag lookups; the response fields are unreliable. The
   header now echoes the user-supplied image_id, falling back to the
   sha256 id only when image_id itself is empty.

2. Ports printed as raw Python dicts ({'port':'22','protocol':'tcp'}).
   The ports array is a list of {port, protocol} objects — each entry
   now renders as "22/tcp".

3. Environment printed as raw Python dicts ({'key':'PATH','value':...}).
   The env array is a list of {key, value} objects — each entry now
   renders as "PATH=/usr/local/...".

cmd, entrypoint, and volumes (plain string arrays) were already
correct and are untouched. Tests updated to match the live shape;
two new tests guard the header fallback. References #4 (already
closed by 0.4.2 — no need to reopen for a rendering polish).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "mcp-synology-container"
-version = "0.4.2"
+version = "0.4.3"
 description = "MCP server for Synology Container Manager"
 requires-python = ">=3.12"
 dependencies = [