[FIX] ServerInfo, MCP initialize advertised stale hardcoded 2.26.0 (issue #27) : read version from package.json as single source of truth

[FIX] GraphicsTools, four image handlers leaked full base64 PNGs into text metadata :
- asset_preview and prefab_render read result.base64 (always undefined through the bridge envelope) so the image block was empty and metadata.data.base64 shipped the whole PNG as text (multi-hundred-KB token bomb)
- material_info and texture_info never image-ified enveloped previews and stringified the PNG into the response
- All six graphics handlers now share one imageResultBlocks() helper (both envelope depths, data-URL strip, base64 removed at both metadata depths)
- Regression test: image block present, base64 never appears in any text block

[FIX] QueuePoll, completed tickets without a result leaked queue metadata (ticketId, agentId) into tool output : return a minimal status object instead; regression test added

[FEAT] DebugLog : UNITY_MCP_DEBUG=1 gate (was unconditional file append + sync I/O on every tool call, unbounded growth) + 5MB rotation; README documented flag is now real

[CLEAN] DeadCode : remove never-imported persistState/loadState/clearState, unused getActivePort and BRIDGE_URL; honest description for the accepted-for-compat refresh param on unity_list_instances

[CLEAN] Docs : README env table (UNITY_BRIDGE_TIMEOUT 60000 not 30000, UNITY_MCP_DEBUG semantics), tool counts corrected to 330+/331 (68 core + 254 advanced) in README and manifest, manifest version synced 2.18.0 -> 2.30.0