BROWSE per-cell validation hook

[DDecoene]

Scope

src/ui/Grid.ts currently has no per-column validation — any typed value commits (see commitEdit()). Add real client-side validation so an invalid edit is rejected inline (cell stays in edit mode with a visible error, or the edit is reverted) rather than silently writing bad data.

• Server needs to tell the client each column's type + constraints. Extend whatever WS message currently carries table structure to BROWSE (check src/shared/types.ts and the grid-open / LIST STRUCTURE message shapes) to include type (CHAR/NUM/DATE/TIME/LOGICAL) and any qualifier (TIME(15), NUM(p,s)). Depends on the TIME type work (TIME column type #43).
• Grid.ts validates client-side before commit, per type:
  • DATE — valid calendar date in the expected format.
  • TIME / TIME(n) — HH:MM, plus minute-granularity check if n is set.
  • NUM(p,s) — numeric, fits precision/scale.
  • LOGICAL — .T./.F. (or the existing boolean literal set).
• Keep server-side validation too (the TIME type validation from TIME column type #43 already covers REPLACE) — the grid hook is a UX improvement, not a replacement for the authoritative check.

Branch

feature/<name> off release/v1.2.0, PR targets release/v1.2.0. Should land after #43 (TIME type) since it validates against TIME columns.

Tests

Playwright coverage: type an invalid time into a TIME grid cell and assert it's rejected/flagged; type a valid one and assert it commits. Extend tests/assistant.spec.ts or add a focused new spec, following existing grid-interaction patterns.

Definition of done

Per CLAUDE.md → Definition of done: tests green (vitest + playwright), CLAUDE.md BROWSE section updated if shortcuts/behavior changed, changelog entry.

[DDecoene]

Merged in #49 into release/v1.2.0.