Depends on:
- https://github.com/odoo/enterprise/pull/127955

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Lay the groundwork for the new design: additional SCSS system variables, generated o-color utility classes, and a reworked control panel (dropdowns, pager, breadcrumbs, search panel resize handle, border-bottom default).

On top of that foundation, refresh the core views themselves; kanban, list, form (statusbar), calendar, graph
(toolbar rework), pivot, activity and hierarchy. Rplace the ad hoc "no content" illustrations across modules with a shared pictogram set.

Most of this exists to give the Enterprise redesign (see the paired enterprise PR) a consistent base to build on, but the views listed above get the same visual refresh in Community as well.

Also includes a couple of unrelated fixes surfaced along the way: nested sortable drop-zone detection near rounded row corners, and a project_todo chatter-panel alignment regression from the border-bottom default change.

task-6330603


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Payslip inputs used to be a system parallel to salary rules:
hr.payslip.input.type records defined what could be entered on a
payslip, payslip-side "payroll properties" stored the per-payslip
values, and rules read them back through dedicated helpers. The same
business value was spread over three models, with duplicated codes,
availability flags and defaults that easily got out of sync.

hr.salary.rule becomes the single source of truth for inputs:

- hr.payslip.input.type is removed. hr.payslip.input and
  hr.salary.attachment reference the rule directly via salary_rule_id,
  and an input line's code is its rule's code.
- Payslip-side properties are removed. Per-payslip values live as
  hr.payslip.input lines; computations read them through the `inputs`
  localdict, keyed by rule code (same-code lines are summed).
  Employee-side values remain as version properties, synced into the
  structure definition from the rules flagged available on the
  employee, whatever their condition type.
- Availability boils down to two flags on the rule:
  input_usage_employee (editable on the employee, stored on the
  version) and input_usage_payslip (usable as payslip input or salary
  adjustment). available_in_attachments, is_quantity and
  default_no_end_date are removed.
- input_default_boolean becomes input_selected_by_default and only
  means: new payslips automatically get an input line for this rule,
  prefilled with its default value (the default is only shown when the
  flag is set). Boolean-typed properties are gone; version properties
  are plain floats.
- A Salary Input rule (condition or amount based on the input) must be
  available on the employee or the payslip, otherwise it could never
  receive a value.
- UI: input options move to a dedicated tab on the rule form; input
  lines prefill their description and value from the rule; salary
  adjustments only propose rules of the employee's structure type and
  warn when no structure of that type consumes the selected rule.

Localizations are converted accordingly: self-consuming python rules
are flagged input_usage_payslip, AU input types become salary rules,
CH/HK/AE/TR property reads go through the inputs localdict, and RO/LT
selection-based benefits become hr.version fields again since
selections cannot be expressed as input lines.

Note for BE: the December double-holiday regularization tests now
assert a non-zero balance. The amount is injected as a real input line
and actually computed, whereas the previous property-based injection
was silently lost before computation.