Task: Add domain-explanation tooltips to Currency and Currency Pair Convention detail fields

Fields like spot_relative and end_of_month aren't self-explanatory from their label alone. Add tooltips explaining the underlying domain concept (not just restating the label) to every field in the Currency and Currency Pair Convention detail dialogs, and — where technically feasible — to the corresponding column headers in their list windows too, so the explanation is available without opening a record.

• [X] Every field in the Currency detail dialog has a tooltip explaining the domain concept.
• [X] Every field in the Currency Pair Convention detail dialog has a tooltip explaining the domain concept (e.g. spot_relative, end_of_month, pip_factor vs tick_size).
• [X] Column headers in the Currency and Currency Pair Convention list windows carry the same tooltips, if the Qt table-header widget supports it (confirm feasibility as part of this task).

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

Neither facet existed in codegen: no per-field tooltip in the detail dialog .ui template, no header-tooltip role in the Qt client model's headerData. Both are generic, reusable additions (any future model gains them for free by adding a tooltip column), not one-off hand-edits:

• Added a tooltip column to the Detail fields org table shape (_detail_fields in org_loader.py already passes any column through generically, so no python change was needed there). Wired qt_detail_dialog_ui.mustache (edited via its org source, ores.cpp.qt.detail_dialog_ui.org, then re-tangled) to emit a toolTip widget property on both the field's QLabel and its input widget, for every field type (line_edit, text_edit, static/dynamic/flagged combo, check_box, spin_box), gated on the column being present.
• Added the same tooltip column to the Columns (Qt model) table shape and extended Client<Entity>Model::headerData (via ores.cpp.qt.client_model_impl.org) to answer Qt::ToolTipRole for columns that set one — Qt's header view shows this automatically on hover, no extra view-side wiring needed.
• Filled in the tooltip column for every Currency and Currency Pair Convention field (both Detail fields and Columns tables), then regenerated both entities' Qt code via compass codegen generate --address ores.cpp.qt.
• Hit and fixed one bug along the way: mustache's default double-brace escaping HTML-entity-encodes apostrophes (currency's → currency's), which is wrong for both C++ string literals and — while not invalid — needlessly ugly for .ui XML content. Reworded the three affected tooltips to avoid the apostrophe rather than change the template's escaping convention for every other field (headers/labels already use the same double-brace form without issue, since none happened to contain an apostrophe).
• Also caught a column-count-off-by-one in the currency_pair_convention Detail fields table while filling it in (too few blank placeholder cells before the trailing tooltip column shifted the text into the wrong header for five rows) — the generated .ui silently had no tooltip for those fields until reviewed and fixed.

Verified by Test Scenario: Verify Currency and Currency Pair Convention tooltips, run manually against the Qt client by the developer.

Added a generic tooltip facet to ores.codegen.entity: an optional per-row tooltip column on both the Detail fields and Columns (Qt model) tables, rendered as a QLabel=/input =toolTip property in the generated detail dialog and as Qt::ToolTipRole in the generated client model's headerData. Filled in for every Currency and Currency Pair Convention field and regenerated.

Verified live via Test Scenario: Verify Currency and Currency Pair Convention tooltips against a rebuilt Qt client — all 8 steps PASSED, confirming every detail-dialog field and list-window column header shows a domain-explanatory tooltip. The first verification run had failed on an unrelated environment issue (the jolly_knuth tenant's Barclays Plc provisioning was missing badge seed data, making every badge render with the shared fallback colour); fixed by recreating the database and re-running the full provisioning script, which is unrelated to the tooltip work itself.