test(example): layered SQLite API sample app (ports & adapters)

[mpyw]

A self-contained sample project under testdata/example (its own module, joined to the root via go.work) that uses bisql the way a real service would: a small HTTP API executing its templates against an in-memory SQLite database (pure-Go modernc.org/sqlite), laid out in clean-architecture layers with manual DI.

src/app/app.go                 application core: struct App aggregates the query ports
src/app/query/                 query ports (one interface per query) + DTOs
src/app/schema/                the Migrator port
src/app/presentation/          HTTP delivery; depends only on *app.App (+ end-to-end test)
src/app/infrastructure/query/  query impl (bisql + database/sql), one file per query;
                               .sql templates under sql/ (embedded); snapshot test + testdata
src/app/infrastructure/schema/ Migrator impl + schema.sql
src/cmd/serve/                 composition root (manual DI wiring)

• Interfaces (app/query, app/schema) are the abstractions; app/infrastructure/* implements them; cmd/serve wires them by hand.
• The queries exercise the full feature set with correct anchoring; presentation_test.go drives the whole stack over a real :memory: DB, proving the bisql-built SQL is valid SQLite.
• Two snapshot kinds per query under testdata/snapshots/: <name>.expanded.sql and <name>.<case>.embedded.sql, regenerated with go test ./... -update.
• The example code is written in samber/lo style (helpers/loops minimized).
• Added to the example module only; the root module is unaffected.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.52%. Comparing base (f3f5c4d) to head (15b94d6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #20   +/-   ##
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  Coverage   96.52%   96.52%           
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  Files          11       11           
  Lines         951      951           
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  Hits          918      918           
  Misses         21       21           
  Partials       12       12           

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