Before, confirming a purchase order automatically created a vendor pricelist (product.supplierinfo) for every product/vendor without one, silently locking the first purchase price in as pricelist.

In industries with constantly fluctuating prices (e.g. oil), purchasers do not negotiate pricelists, they simply apply the last price communicated by the vendor. For them, the pricelist automatically created on order confirmation was outdated by the next price change, and maintaining pricelists could be tedious.

Now vendor pricelists are only created manually.
When no pricelist is defined for a product/vendor, the most recently confirmed purchase order line acts as the vendor pricelist.

Additionally, the purchase history / price comparison view gains an optional 'Discount %' column, and is grouped by vendor by default.

_select_seller now returns the seller information as a dictionary
instead of a product.supplierinfo record, since a seller can come
from the last confirmed purchase order line, which has no record.

task-5456444

For details, see the docs in the related task.

As a general ides, this PR aims at simplifying the management of Lump
Sum Allowances. We first refactor the Representation Fees section in the
Payroll tab of the employee form view by switching from using checkboxes
with their related fixed amounts, to using editable fields that have
their defaults fixed to those amounts. We then introduce new categories
to include a miriad of other possible allowances. Finally, we integrate
this with the new view_id system so that each lump sum can be
activated/deactivated at will.

All Benefits under the Lump Sum Allowances section except for Daily
Misc. Other Criteria and Monthly Misc. Other Criteria are considered
normal Representation Fees (i.e. with serious standard). Each of them
has their own Salary Rule with category SERIOUS_REPRESENTATION, all
these values are later grouped (summed) in the Representation Fees
salary rule. In the same way, Daily Misc. Other Criteria and Monthly
Misc. Other Criteria have their Salary rules with category
NON_SERIOUS_REPRESENTATION and are summed to become
Representation Fees (Without Serious Standard). Representation fees
with serious standard are fixed amounts, while those without serious
standard are prorated based on the amount of days in the payslip
period that are eligible for representation fees.

Some Benefits (namely Homeworking, Phone, Internet, all the Car
Management ones and the Daily and Monthly Misc. ones) are only based on
the amount set on the employee's profile. The other
benefits are based on both the value on the employee profile and a
Salary Input on the payslip, that specifies either the distance traveled
or the days of outside work depending on the type of benefit.

We also have to modify some tests that were failing because they were
expecting different rules to appear in the payslip and a threshold to
the With Serious Standard amount.

Task: 5443155

Improves AI-generated page quality, and splits a full-page build in two so it
fits the worker time limit.

- **Art direction** - new `apply_brand_kit` tool (palette, font pairing,
  corners/shadows); the prompt now picks an aesthetic direction and layout
  before writing HTML.
- **Refinement passes** - after a page is composed, two one shot passes add
  section shapes and CSS polish. The LLM returns decisions only, markup is built
  in Python so rules it ignores can be enforced.
- **Snippets** - explicit allowlist with intent hints, shuffled so picks rotate.
- **Images** -  written as `<img data-ai-image-prompt>` and generated during
  finalization.
- **Deferred finalization** - images and both refinement passes moved to
  `/ai_website/finalize_page`. Page and reply are held server-side and released
  together, so only the finished result is shown.

**Why split:** `- limit-time-real` (120s) killed the worker, at least on runbot, so image generation, refinement passes are not part of the main loop anymore and are a separate request. worth looking at if another solution would be available