Add lightweight read modes #3953

Is your feature request related to a problem? Please describe.
The Memory MCP server's read_graph tool returns ALL entities with ALL observations in a single response. Over time, as observations accumulate (weeks/months of usage), this creates critical scalability issues:

1. Context Explosion: A single memory_read_graph call can consume 50k-80k+ tokens, overwhelming the model's working context. After 6 weeks of daily usage, my graph has 150 entities with 800+ observations.
2. No Progressive Loading: There's no way to fetch entity names first, then selectively load observations. Even simple status checks like "what applications are queued?" require loading the entire graph.
3. Observation Bloat: No built-in mechanism exists to split, archive, or reorganize oversized observations into new entities. Users must manually edit memory.jsonl files or lose historical data.
4. Forced All-or-Nothing Reads: Current tools (read_graph, open_nodes, search_nodes) all return full observations with no pagination, filtering, or metadata-only modes.

This is a scalability blocker for long-running MCP memory server deployments. Without these features, users must either:

• Manually prune memory.jsonl files (losing historical data)
• Reset graphs frequently (losing context continuity)
• Accept degraded model performance as graphs grow

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1. Lightweight Read Modes (Enhance Existing Tools)
   Add optional parameters to existing tools:

// ENHANCED: read_graph with options
read_graph(options?: {
  includeObservations?: boolean,  // default: true
  observationLimit?: number,      // max observations per entity
  entityTypes?: string[],         // filter by entity types
  metadataOnly?: boolean          // return only name + entityType + observationCount
})

// ENHANCED: open_nodes with options
open_nodes(names: string[], options?: {
  includeObservations?: boolean,  // default: true
  observationLimit?: number,      // paginate observations
  observationOffset?: number      // for pagination
})

// ENHANCED: search_nodes with options
search_nodes(query: string, options?: {
  includeObservations?: boolean,  // default: true
  limit?: number,                 // max entities to return
  observationLimit?: number       // max observations per entity
})

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