feat(telemetry): add wire-format module and export event reader

[EhabY]

Summary

• Introduce src/telemetry/wireFormat.ts as the single source of truth for the on-disk JSONL telemetry shape. SessionContext, TelemetryContext, and TelemetryEvent are now DeepReadonly<z.infer<...>> derived from schemas, so the wire format and the TS types cannot drift.
• serializeTelemetryEvent and parseTelemetryEventLine are shared by the sink (writer) and the exporter (reader); the sink's hand-rolled serializer is gone.
• Add listTelemetryFilesForRange (filename-date filtering, chronological order) and streamTelemetryEvents (line-by-line AsyncIterable<TelemetryEvent> with TelemetryFileParseError for parse failures).
• Add range.ts with createPresetDateRange, createCustomDateRange, validateUtcDateInput, isTimestampInRange, and fileDateCanContainRangeEvent. Preset table is the source of truth for TelemetryRangePresetId and the UI-facing TELEMETRY_RANGE_PRESETS.

Refs #903.

Stack: 1 / 4. Next: #960.

Notable design choices

• Schema is the source of truth: SessionContext/TelemetryContext/TelemetryEvent come from z.infer<...> wrapped in a local DeepReadonly<T> so nested fields (including context, properties, measurements, error) stay readonly all the way down. event.ts re-exports the types for back-compat.
• Wire and in-memory shapes are kept aligned by a single tiny wireToCamel helper that renames structural keys (top-level + context); properties and measurements pass through verbatim since they hold caller-supplied keys.
• Parser tags failures with TelemetryFileParseError so stream readers can distinguish parse errors from IO errors without sniffing message text.
• Filename pattern is loose on the session slug but anchored on the date (which is all we need for filtering); the comparator orders by (date, session, part).
• Half-open UTC ranges; fileDateCanContainRangeEvent is a coarse calendar-day filter so files outside the window are skipped without being opened.

Tests

• New test/unit/telemetry/wireFormat.test.ts covers serializer behavior (snake_case top level and context, optional-field omission, arbitrary properties/measurements keys), round-trip serialize→parse, TelemetryFileParseError tagging with source:line, and rejection of invalid ISO timestamps and missing structural fields.
• test/unit/telemetry/export/files.test.ts (memfs-backed) covers date filtering, missing-directory handling, timestamp-range streaming, and parse-error surfacing with file:line context.
• test/unit/telemetry/export/range.test.ts covers preset and custom range construction, UTC validation, and the calendar-day pre-filter.
• test/unit/telemetry/sinks/localJsonlSink.test.ts migrated to the shared createTelemetryEventFactory and no longer maintains its own event fixture.