fix: auto-convert project name in settings & consolidate code

[elias-ba]

Description

Fixes the project settings form to auto-convert project names to URL-safe format (lowercase, hyphens, digits), matching the behavior of the project creation form. Previously, entering a name like "DEP-burundi-datafi" in settings would fail validation since the form submitted the raw input directly.

This PR also consolidates all duplicate coerce_raw_name_to_safe_name functions into Project.form_changeset/2 and Project.form_with_users_changeset/2, using a virtual :raw_name schema field. This follows the pattern already established by Collection.form_changeset.

Along the way, a pre-existing bug was fixed in the dashboard creation modal where the save error path assigned to :project_changeset instead of :changeset, meaning validation errors from failed project creation were silently swallowed. Additionally, the @name assign is now initialized in update/2 (previously it only got set after the first validation event), and whitespace inside the name preview badge <span> tags was cleaned up to remove a trailing space.

Closes #4437

Validation steps

Project settings

1. Edit the project name with uppercase/spaces (e.g. "My Cool Project")
2. Verify the preview badge shows my-cool-project
3. Save and confirm it persists the slug name
4. Clear the name and verify a single "can't be blank" error (not duplicated)
5. Change retention settings and verify the name does not break

Create New Project

1. Type "Hello World!" and verify badge shows hello-world
2. Clear the name and verify submit disables and a single error shows
3. Submit and verify the project is created with the slug name

Create / Edit Sandboxes

1. Create with "My Sandbox" and verify badge shows my-sandbox
2. Create another with the same name and verify "Sandbox name already exists" error
3. Edit a sandbox and rename it

Create / Edit Collections

1. Create with spaces/uppercase and verify slug preview
2. Edit an existing collection and verify name displays correctly

Create / Edit Projects (superuser interface)

1. Edit name to uppercase and verify preview updates
2. Save and verify slug persists

AI Usage

• I have used Claude Code
• I have used another model
• I have not used AI

Pre-submission checklist

• I have performed an AI review of my code (we recommend using /review with Claude Code)
• I have implemented and tested all related authorization policies. (e.g., :owner, :admin, :editor, :viewer)
• I have updated the changelog.
• I have ticked a box in "AI usage" in this PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.43%. Comparing base (32f1001) to head (eb71080).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4436      +/-   ##
==========================================
+ Coverage   89.33%   89.43%   +0.10%     
==========================================
  Files         425      425              
  Lines       20133    20147      +14     
==========================================
+ Hits        17985    18018      +33     
+ Misses       2148     2129      -19     

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[stuartc]

Some issues, mostly around the validation not being tested - and errors not shown probably (raw_name doesn't have a schema so I can't see it getting errors?).

Also there is a smell around the copy pasting of coerce_raw_name_to_safe_name, not just in this PR, in other places. There are 5 different files with an almost copy paste of this kind of function. I first thought we should put the transform into the schema, but then thought that might cause rendering weirdness with the schema changing the input - Collection has a form_changeset function that handles the :raw_name and the model has that as a virtual field. Keeping the logic a model concern and not a view concern.

[elias-ba]

Thanks @stuartc, great catch on all fronts. I've reworked the PR following your suggestion to use the Collection pattern. Project now has a virtual :raw_name field and a form_changeset/2 that handles the derivation at the schema level, so all copies of coerce_raw_name_to_safe_name are gone. Errors on :name get copied back to :raw_name so they show up on the visible input. Also extracted a shared <.name_badge> component since the preview badge was duplicated across all the forms. I think this now looks way better, thanks a lot again. Would you mind having another look ?