feat(nql): GROUP BY aggregates + VALID AS OF + TRACE in browser mock parser

[Eth-Interchained]

Summary

• Extends src/lib/nql.ts mock NQL parser to handle three clauses the engine has supported since v1.0.0 but the browser parser rejected with "unexpected trailing input": GROUP BY + aggregates, VALID AS OF (both positions), and TRACE [REVERSE].
• Plan interface grows five new fields: validAsOf, trace, traceReverse, groupBy, aggregate.
• executeNql now runs all five aggregate functions (COUNT, SUM, AVG, MIN, MAX) against seed data in-browser.
• TRACE executes a forward/reverse linked-list walk via the named field in mock mode; adds a note directing users to the live engine for full sealed causal chains.
• VALID AS OF adds an informational note in mock mode (full valid-time indexing needs nedbd).
• Grammar docstring updated to reflect the full v1.0.4 engine grammar.
• Updates COMMITS.md and ideas.md for the next maintenance turn.

Why this matters

Queries like FROM orders GROUP BY status COUNT or FROM events TRACE caused_by REVERSE are valid NQL that the live engine handles correctly. Before this PR they threw a parse error in Studio mock/offline mode, breaking the playground experience for these three clause families. Post-PR, Group By aggregations execute fully in-browser; VALID AS OF and TRACE pass through with informational notes.

Engine impact

None — pure Studio TypeScript change, no nedbd routes affected.

Studio impact

• src/lib/nql.ts — parser + executor extended; Plan type widened.
• Downstream code that uses Plan benefits immediately: the console no longer shows red parse errors for GROUP BY / VALID AS OF / TRACE queries.

Tests run

25 new mock tests pass (Node ESM, no build step required):

• 12 parse-level checks: all new clauses, combinations, full kitchen-sink query
• 3 error-path checks: missing field, missing SUM argument, trailing garbage
• 10 execute-level checks: COUNT/SUM/AVG/MIN/MAX aggregation, WHERE + GROUP BY, group count

Result: 25 passed, 0 failed

TypeScript types are consistent — no new any casts introduced; AggFunc union type exported for downstream use.

Follow-up work

1. Files API proxy — expose nedbd /files + /files/:filename + /files/:filename/root through Studio Express; add Files tab in Databases page (Merkle root display enables ITC/BSC anchoring).
2. Checkpoint button — POST /:name/checkpoint proxy + UI button in Database detail view.
3. Engine: reconcile pyproject.toml license — still declares Apache-2.0 but LICENSE is BSL; fix metadata to avoid package-index confusion.