JQL-style text query language for issue search

Split out of PAR-191 (operator filter builder + saved views shipped). A power-user text query as a third layer over the same predicate model.

Scope:

• A small parser: assignee != "Rían" AND priority >= high AND label = bug → the Condition[] model in lib/filters.ts (extend with range ops for priority/dueDate).
• A query input that round-trips to/from the builder chips and the URL f param.
• Reuse conditionSql in lib/sql/issues.ts (already parameterised); add before/after (dueDate) and >=/<= (priority) operators.
• Validation + friendly parse errors.

Builds entirely on PAR-191's model; no backend (Java) change — issue-list filtering is mirror-side (Kysely).