docs: add event schema and Dune analytics guide (#80)

* docs: add event schema and Dune analytics guide

* fix(dune): use correct Dune Stellar column names

topic_1/data do not exist in stellar.history_contract_events.
The real columns are:
  topics_decoded  VARCHAR  JSON array — index 0 is the event-name symbol
  data_decoded    VARCHAR  JSON object — keyed by field name

Replace all topic_1 references with:
  JSON_EXTRACT_SCALAR(topics_decoded, '$[0]')

Replace all data references with:
  JSON_EXTRACT_SCALAR(data_decoded, '$.field')

Fix applied to all 10 .sql files and the matching code blocks in
docs/dune-analytics.md. Also add correct column table to §1.

* ci: run verify-build on docs changes so docs-only PRs satisfy the required check

The build job only triggered on contracts/** and toolchain paths, so a
docs-only PR never ran it — and since build is a required status check,
those PRs were unmergeable (BLOCKED with 'build expected', not even
admin-overridable). Add docs/** to the triggers: build recompiles the
contract (a no-op pass for docs) and the required check is satisfied.

Also brings this branch up to current testnet.

---------

Co-authored-by: Collins Ikechukwu <collinschristroa@gmail.com>

Author: ryzen-xp

.github/workflows/verify-build.yml

@@ -7,6 +7,7 @@ on:
       - testnet
     paths:
       - 'contracts/**'
+      - 'docs/**'
       - 'Cargo.toml'
       - 'Cargo.lock'
       - 'rust-toolchain.toml'
@@ -23,6 +24,7 @@ on:
       - testnet
     paths:
       - 'contracts/**'
+      - 'docs/**'
       - 'Cargo.toml'
       - 'Cargo.lock'
       - 'rust-toolchain.toml'