Filings UI: there should be different error dialogs depending on why the dashboard is unavailable

### Title: Dashboard Unavailable

----

## Description:
* As a user
* I want specific information on why my business dashboard is unavailable
* so that I can correct my mistake if it's my fault or retry/exit if it's something else.

**Acceptance Criteria**
* Given I have the necessary Keycloak tokens
* when I try to access the business dashboard without a business identifier
* then I should see a specific error dialog telling me I'm trying to do something invalid (ie, loading the dashboard without a business ID) instead of the generic message telling me that I can't access my dashboard and that I should try again later.

**Dependencies? (If so, link dependency in the ticket, make it visible in a team´s backlog)**
N/A

**Validation Rules? (If yes, list here)**
N/A

----

**DoR for User Story:**
- [ ] Do we have a prioritized Sprint Backlog?
- [ ] Defects, user stories and other work the team has committed to are contained in the sprint backlog?
- [ ] Any hidden work?
- [ ] All team members availability (days) & capacity (in SP) is known for the Sprint?
- [ ] All users stories meet the DoR?

**Definition of Ready:**
1. [ ] Does User Story have full flow of business rules, happy and alternate paths, etc.?
2. [ ] Requirements & expected behavior included in the User Story?
3. [ ] Are the dependencies known/ understood?
4. [ ] Dev team accepts user experience artifacts
5. [ ] If there are validation rules, are they defined (UI, Data, Role-Action)?
6. [ ] Does this User Story needs stakeholder approval?
7. [ ] Is this user story small enough to be completed in a Sprint?
8. [ ] What do we possible have to do re Change Management? - a) GCPE, …?

----

**Definition of Done:**
1) [ ] Check Requirements against completed tasks
2) [ ] Completed stories verified in Dev and Test
3) [ ] Confirm Test cases built and succeeding
4) [ ] No regression test failures
5) [ ] Test coverage acceptable by Product Owner???
6) [ ] Ticket merged to master or story branch
7) [ ] Developer to list Config changes/ Update documents and designs
8) [ ] Design / Solution accepted by Product Owner
9) [ ] UX Approved
10) [ ] Can be demoed in Sprint Review
11) [ ] Release ticket is created and this US is linked to it

Start by locating the Filings UI business-dashboard access flow and the handling for requests with Keycloak tokens but no business identifier. Verify the current generic unavailable dialog for that scenario, then confirm that the missing-identifier case shows a distinct corrective message while other unavailable cases retain their retry or exit guidance.

Written by the indexing model from the issue text.