**Contract Amendment & Versioning Logic**

* When an offer's contract start date falls within an existing contract period, it is treated as a contract amendment (new version) rather than a new contract.
* For contract amendments, the offer's contract end date is read-only and automatically inherited from the existing contract.
* When creating a new offer, any existing versions with effective dates **on or after** the new offer's contract start date are automatically archived, as they likely contain outdated data.
* Added a warning to notify users when a new offer will replace existing future versions.

**Technical Refactoring**

* Simplified the `employee_version_id` computation by delegating to the existing `_get_version` method on the employee model. This ensures the selected employee version correctly matches the contractual state effective at the new offer's
* Ensured cache invalidation after rollback savepoints to prevent stale data. The overridden `_get_version` in `hr_contract_salary_payroll` writes to `employee.version_id` and the `contract_template_id`; although rolled back, it polluted the cache. We now always invalidate the cache after rollbacks to avoid inconsistencies, including later module installation.

**Simulation & Chatter**

* Inside the simulation, when calling `_get_version`, we need to adjust the contract dates of the version being simulated. The main challenge is allocating this simulated version between existing employee versions without creating contract overlaps, since overlaps raise validation errors.
* To avoid this issue, we move to a new approach. We archive all versions after `employee.version_id` and set `employee.version_id.contract_date_end = False`.
* Then, instead of replacing the active version, we create the simulation version as an amendment to `employee.version_id`. The amendment's effective date is set to `max(fields.Date.today(), employee.version_id.contract_date_start, self.contract_start_date)` + 1 day. This ensures the current version remains unchanged, avoids contract overlaps, and prevents chatter pollution.

task: 5408192

Currently when creating a subscription for a service product, if the minimal period is a multiple of the time unit: eg two week, three months, etc... The discount amount ends up wrongly computed.

The reason for that is that discounts for services are computed by taking the price of the minimal period and then comparing it to other prices, however that base price is not scaled down to single units of time like the compared prices are. https://github.com/odoo/enterprise/blob/9eac36e4d981fd6062702e7119c664ac7951d613/website_sale_subscription/models/product_template.py#L130-L135 https://github.com/odoo/enterprise/blob/9eac36e4d981fd6062702e7119c664ac7951d613/website_sale_subscription/models/product_template.py#L204-L205

**Steps to reproduce:**

- Create a service subscription product
- In Recurring Prices, select or create a recurring plan that is a multiple of a unit of time, ex 2 Months
- Create two entries, one with the created plan and one with a plan that spans a longer period, ex 1 Year
- Set the prices, ex 100 and 600
- Click 'Go to Website' and you'll observe that both are 50% off

opw-6107509

**Steps to reproduce**
- Create a first partner (name: "Partner", email: "partner@mail.com", phone: "123").
- Go to the website form of a helpdesk team, and submit a ticket using "Partner@mail.com" as email (notice the different capitalization) and "456" as phone number.

Behavior without this fix: a new partner is created, but the ticket is assigned to the orignal partner ("partner@mail.com") and its phone number is updated.

Behavior after this fix: no partner is created.

**Causes**
- the partner search was case sensitive
- the created partner was not used as the `partner_id` of the ticket as it was added to the params but needs to be in the kwargs passed to `handle_website_form` in order to be found used by `extract_data`. The original partner was found in `_find_or_create_partner` by the call to
`_mail_find_partner_from_emails` (case-insensitive)

Note: this commit also ensures consistency between the partner's company and the ticket's company (same as in `_find_or_create_partner` of `helpdesk.ticket`).
Also, avoid allowing modifying existing partner's phone via this form.

opw-5914064

Forward-Port-Of: odoo/enterprise#109393