[Node] Wire: max-level, neighbor, and set-link event handlers

[thep2p]

Summary

Wire the 5 process_incoming_event arms that are pure local queries or waiter-resolves: GetMaxLevelOp, RetMaxLevelOp, GetNeighborOp, RetNeighborOp, SetLinkOp.

Reference

Algorithm detail: docs/protocol/concurrent-insert.md, Sections 3.1 and 3.2.

Scope

• src/node/base_node.rs — 5 new match arms in EventProcessorCore::process_incoming_event.

Acceptance Criteria

• GetMaxLevelOp and GetNeighborOp answer directly from local table state, with no forwarding.
• RetMaxLevelOp, RetNeighborOp, and SetLinkOp each resolve the correct pending waiter by Nonce, no-op (not an error) if no waiter is found, matching the existing SearchByIdResponse resolve-or-no-op structure; additionally emit a trace log on the no-waiter path (a new addition — SearchByIdResponse today does not log this case).
• One test per arm (5 tests total).

Depends on

• [Network] Add: join/repair Event variants and payload structs #84
• [Node] Generalize request correlation: add Phase 0 join bootstrap #88

Dependency graph (unblocked first):
EPIC #81 -- local search & join protocol
  #67 [DONE] search_by_id            #71 [OPEN] search_by_mem_vec (independent)
  #74 [OPEN] search_by_id timeout fix   #76 [OPEN] delete/leave
  Concurrent join + repair (Algorithm 2 + Algorithm 8; supersedes closed #66, #77):
    L0 (no deps):         #84  #85  #93  #86  #87
    L1:                   #94  #88  #89
    L2:                   #90  #91 <-- YOU ARE HERE  #95  #96
    L3:                   #92
    L4 (acceptance gate): #97