Add aggregate Lightning balances to node info

[Kewe63]

Summary

• add aggregate outbound_balance_msat and inbound_balance_msat fields to /nodeinfo
• include only channels whose /listchannels status is Opened
• document both fields in the OpenAPI schema
• add regression coverage for empty, opening, ready-but-closing, and multi-channel states

---

Implementation

A channel contributes to the aggregate only when it is ready and not shutting down. This matches the existing ChannelStatus::Opened classification used by /listchannels.

The returned values are the sums of LDK's outbound_capacity_msat and inbound_capacity_msat values for those channels.

---

Validation

• cargo +1.94.0 fmt -- --check
• Clippy with -D warnings across all 9 CI feature combinations
• cargo +1.94.0 test aggregate_balances_excludes_channels_that_are_not_opened
• cargo +1.94.0 test multi_hop --no-run
• OpenAPI YAML/schema validation
• git diff --check

---

The local multi_hop integration run passed the new /nodeinfo aggregate assertions, then failed later at the pre-existing balance assertion on src/test/multi_hop.rs:258.

Fixes #70

[codecov]

Codecov Report

❌ Patch coverage is 96.77419% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.77%. Comparing base (e400827) to head (5576a5a).

Files with missing lines	Patch %	Lines
src/routes.rs	96.77%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #168      +/-   ##
==========================================
+ Coverage   87.72%   87.77%   +0.04%     
==========================================
  Files          16       16              
  Lines        8459     8490      +31     
==========================================
+ Hits         7421     7452      +31     
  Misses       1038     1038              

Flag	Coverage Δ
rust	87.77% <96.77%> (+0.04%)	⬆️

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