docs: refresh stale architecture and structure docs

[pinebit]

Updates docs/architecture.md, docs/structure.md and the CLAUDE.md architecture summary to match the current implementation.

docs/architecture.md:

• Keeps both ASCII diagrams; removes the Signer/remote-signer component from the workflow diagram (it does not exist in the code) and corrects the BFT fault tolerance note to t = ceil(2n/3) available and honest nodes, tolerating f = floor((n-1)/3) faulty nodes.
• Updates all interface snippets to match core/interfaces.go (Scheduler, Fetcher, Consensus + ConsensusController, DutyDB, ValidatorAPI, ParSigDB, SigAgg, AggSigDB, Broadcaster) and notes that file as the source of truth.
• Scheduler: bulk cached validator resolution, sync committee and derived aggregator/sync-contribution duty scheduling, slot offsets, SSE head/reorg event handling, builder registration submission.
• Consensus: documents the pluggable consensus controller with QBFT v2.0 as default and priority-protocol-based selection, linking to docs/consensus.md.
• DutyDB/ParSigDB/AggSigDB: replaces outdated relational data models with the actual in-memory designs, inline threshold matching and deadliner-based trimming; resolves stale TODO/open questions.
• Validator API: replaces the outdated endpoint list with a table of currently intercepted endpoints and updates the SignedData implementations list.
• Adds a duty lifecycle table (initiator, consensus, broadcast per duty type) and a supporting components section (Tracker, InclusionChecker, Priority/InfoSync, Deadliner, duty gater, caches, builder registration service).

docs/structure.md:

• Removes references to deleted code (core/encode.go, app/dbindex/, p2p/discovery.go/discv5) and describes relay-based peer discovery.
• Adds missing packages (core/consensus, core/tracker, core/priority, core/infosync, app infrastructure libraries, eth2util and testutil subpackages) and the current CLI command tree (combine, exit, deposit, feerecipient, alpha, unsafe).

CLAUDE.md:

• Aligns the architecture summary with the refreshed docs: pluggable consensus controller, corrected Priority and peer discovery descriptions, adds the InclusionChecker.

category: docs
ticket: none

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.22%. Comparing base (6ffb9bb) to head (5f116ee).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4580      +/-   ##
==========================================
+ Coverage   57.20%   57.22%   +0.02%     
==========================================
  Files         245      245              
  Lines       33449    33449              
==========================================
+ Hits        19135    19142       +7     
+ Misses      11890    11880      -10     
- Partials     2424     2427       +3     

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