[FIX] chart: prevent line chart value labels from clipping

[rmbh-odoo]

Description:

Current behavior before PR:

• Line chart value labels were clipped at chart edges.
• First and last points could cut horizontally at left/right.
• Top-most points could cut vertically at the top boundary.
• Positioning relied on clamp, causing labels to stick to borders.

Desired behavior after PR is merged:

• Implement smart boundary-aware positioning for line labels.
• Flip label below point if it cannot fit above.
• Add horizontal edge detection and adjust textAlign dynamically.
• Preserve existing bar chart behavior and layout settings.

Task: 5993132

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

[robodoo]