paid-media: missing `title` on nested leaf properties in 3 fieldgroup schemas

[ejsuncy]

Problem

Several nested-object leaf properties in the XDM paid-media fieldgroup schemas are missing the title keyword (and description in most cases). When these schemas are materialized into a CJA dataview, the affected components fall back to displaying the full dot-notation schemaPath as their name (e.g. paidMedia.attributionMetrics.crossDeviceAttribution.devicePathBreakdown.mobileToMobileApp) instead of a human-readable label.

Sibling properties at the same nesting level all have title set, so this looks like an oversight in 3 inline object definitions rather than an intentional pattern.

Detection

Spotted while comparing a CJA paid-media dataview against the source schemas: 41 components in that dataview have name == schemaPath, and all 41 fall into the 3 groups listed below.

Affected fields

components/fieldgroups/paid-media/core-paid-media-attribution-metrics.schema.json

• xdm:devicePathBreakdown leaf properties — mobileToDesktop, desktopToMobile, mobileToMobileApp (no title, no description)
• xdm:channelSequence.items properties — channel, position, weight (no title, no description)

components/fieldgroups/paid-media/core-paid-media-campaign-details.schema.json

• xdm:dayParting.schedule.items properties — dayOfWeek, startHour, endHour (no title, no description)

Fix

Add title and (where useful) description to each of the above leaf properties, matching the style and tone of the sibling fields already present. Per CONTRIBUTING.md: "Provide a description and title for each schema and each property".

No breaking changes — the wire-format property names are unchanged; only title/description metadata is added.